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HBHBBB 0» THB LITBBPOOt tIT. i.HD PHII,. 80C TORKBn PWir mnn .<«. .-. . 0» CAHADA, COBBKSPONDIirS MBMBEB o/thB BMBX TO JSsTWnTM^wn ^i-"*** BVIFALO BAT. HI8T. SOC. PE0FBS80B OF BAT."S CBXV COlt " OM«o" I n , It has of late years, been the aim of philosophical botanists to estab- lish a few general laws of vegetable structure, capable of explaining all the phenomena which fall under our observation, so as to exhibit a eonamon plan in all the various fosms of plants, and show the kind of variations from the general type which occur in each particular in- stance, or in other words, to trace to the action of intelligible causes the peculiarities observable in each distinct structure, so as to show what is common to many, and how mutual relations are manifested ia the midst of apparent diversities. This is, perhaps, to be accounted the highest and most interesting part of the study of nature, and if it must necessarily be preceded by the examination of the details of in- dividual structures, always varied, curious, and attractive, it at least anses out of them as naturally as the philosophy of every science arises out of its facts and observations, combined and meditated upon by the highest intelligences amongst its votaries, aided at times by the happy thoughts of humbler labourers injthe same field. I design now W^' 2 ON CHORISIS. to bring under consideration one of the principles which has been pro- posed as a general expression of a number of facts in the structure of flowers, or, as a cause which may be assigned in explanation of some remarkable features belonging to particular flowers, explaining at once the relation to the common plan, and the meaning of the apparent descrepancy in the special case. My subject is what was, I believe, first named by the French botan- ist Dunal, chorisis, a Greek word expressing division or separation&nA applied to supposed cases of a single organ in a floral circle being, so to speak, resolved by subdivision into a number of parts. At present, whilst many high authorities admit this principle as affording the true explanation of some remarkable facts in the structure of certain flowers, other authorities of not less general weight entirely reject the principle as unsupported by any sufficient evidence, and not needed to explain the phenomena. In such a case any contribution towards determin- ing the point in dispute may be received with patience and may have some claim to attention. It may be expedient in the first place to con- sider what are the principles in relation to^the structure and variation of flowers which may be regarded as known and established, and to what extent they go in explaining* the appearances before us that we may be prepared to judge how far further assistance is required, and, if so, how far the proposed principle sup)>lies what is wanted : nor will this view of what may be said to have been accomplished in an im- portant field of enquiry be in itself destitute of utility since compara- tively few years have changed the whole aspect of botanical science^ and our greatest practical botanists continue to employ in decsription, terras founded on erroneous opinions, and suggesting false vi-ws v^ere on so many accounts the utmost correctness of language is denv. ?(\, besides that the truths to be enumerated, though well established and admitted by those esteemed the best judges, are by no means so gene- rally received and applied as not to require to be explained and en- forced. The 1st principle to be noticed is that every flower originates in an ordinary bud modified in its development, the increase of the axia being checked and the leaves reduced into circles and made to assume. the characteristic forms of floral organs, which setting aside interme- diate end anomalous ones are 4, described and named as follows : thft exterior one, usually retaining most of the leafy charactergCalled as a. whole the calyx, and its separate organs named sepals : within it an- ON CHORI8IS. 3 other set of protective or enveloping parts, usually of a more delicate texture, and more likely to be colored, called the corolla, and its parts petals ; then a set of organs so transformed as for the midrid to be- come a simple support called Wie filament, the lateral expansion to be contracted into cells forming the anther, whilst the superficial cells of its infolded surface are specialised into sperm cells called pollen. These organs as a whole are called androecium and singly stamens. In the remaining circle the leaves are made to bear on their margin or at their base germ cells called ovules, this expanded portion of the leaf or of several such leaves united being the ovarium ; the apical portion gene- rally drawn out to some length, is the style, and the naked glandular tip is the stiffma. The whole circle of these leaves is the gynoecium, individually they are carpels. As there are four distinct modifications of leafy organs, forming in typical examples as many circles, there is a manifest convenience in having a name for each circle as a whole and for the parts of each, besides any names required to designate special por- tions of each organ. I have adopted names from good authority using care in their selection. The chief thing to be observed is the use of the term gynoecium for the whole of the inner circle and car. pel for each separate part. I have judged it necessary to reject en- tirely the Linnaeau term pistil, because, the true theory of the struc- ture of the flower not being then understood, he used the term, some- times for the whole circle of carpels when so united as to seem a single organ ; sometimes for each separate style where the ovarian portions of the carpels are united, but their styles distinct, and sometimes for each carpel where they remained entirely separate, the word is useful enough in reference to the Linnsean artificial system, but cannot be employed to express what is now known without being a source of confusion. It is much to be regretted that eminent teachers of the' science will persevere in employing it, especially as the evil is greatly aggravated by attempts to give the term a new meaning or to persuade us that Linneeus employed it in accordance with our modern ideas. 2. Havinj, considered what seems well established, respecting the origin of the flower and the nature of its parts, what first claims our notice is the variation in the number of circles. We have mentioned four differing in kind, but we may have one, two, or three of these absent, and we may have them increased by the occurrence of many circles of one kind of organ. The difference is in the development of the axis of the flower, which varies from a single W{\ ■ m ON CBCRI818. circle to an indefinite number, the increase being chiefly in the inner ones. Whenever a flower preaents a crowd of similar organs, whether manifestly in successive circles, or by their closeness thrown into a con- fused mass, the explanation which first occurs to the botanist is multi- plication of the circles, whether there may be sometimes reasons for rejecting this and seeking another may be afterwards considered. 8. Our third principle relates to the position of the circles. The most natural and general is with the parts of each (the numbers con- forming) alternate with those of the circles without and within it. This evidently depends on the same spiral plan of growth which produces 'the arrangement of leaves on a stem, the members of the successive circles being indeed produced in the same plane, but when some growth becomes necessary to obtain space for another circle, the advance of the axis being as usual spiral, and to a degree just sufficient to make the parts alternate, but besides that a whole circle may be so nearly sup- pressed by close pressure, as to be scarcely, if at all, perceptible, which would make those immediately within and without appear opposite, the alternation being maintained by the unnoticed intermediate circle, •which is doubtless the true explanation of the stamens opposite to the petals in the Primrose family , it is quite conceivable that in certain ^ases the spiral course might be either prevented, or carried too far for alternation, the parts thus becoming opposite and abnormal examples occurring in which this is seen to take place, proves that we are justi- fied in assuming it as a sufficient explanation of the rare instances in "which adjoining circles with opposite parts occur. Dr. Lindley has justly appealed to varieties of Camellia, in which the petals are ranged in regular lines, giving the flower a star-like aspect as proof of the possibility of the opposite arrangement taking the place of the alter- nate, and those who think otherwise are driven to the most extrava- gant suppositions to evade the force of his argument. But I must af- terwards recur to this subject in another connection. At present I wish to show the real nature of the law of alternation, and the possi- bility of deviation from it in exceptional cases, without disturbing our idea of the plan of structure or driving us to imagine other causes in operation. 4. The degree and mode of development of the separate leafy organs which form each circle may vary from the smallest to the fullest ex- tent, and through several remarkable differences of form. All the parts of the flower consist of leaves modified in their devolpment, and ON CHORI8I8. fC each is capable of assuming any of the functions, for we have mon« strous examples (and I quote none but what I have seen) of carpels occurring among the exterior parts of a half-transformed bud, petals and imperfectly-formed stamens being found within ; of stamens with anthers present having stigmas at their tips and imperfect ovaries at their lower portion ; of petals and stamens passing by all degrees intoi each other and of all the circles returning to leaves. Besides these there are well-known intermediate conditions such as used to be called nectaries, and besides the expanded or unfolded condition of an organ, tubular, hooded, and spur or horn-like enlargements are not unfrequent- ly met with. The leading effects of varying development may, in ad- dition to what has been already pointed out, be conveniently noticed under the following heads, connection or separation of parts ; equality or inequality of the parts of a circle, and influences on the number of parts. As to the first of these, it is a law of vegetable structure, that portions of growing plants, whether of the same, or of closely allied kinds, being in contact and continuing so, for a time without agitation, . will form tissue so as to unite and become as one. This law prevails in the parts of flowers as elsewhere. The result is coherence when or- gans of the same circle unite by their edges, adherence when organs of adjoining circles unite by their surfaces. Increased development of the parts promotes coherence ; closeness of the circles promotes adher- ence, and differences in these particulars have much to do with the variations of the common plan of flowers. We need not, however, be in any doubt as +0 the true explanation of what occurs, as we are familiar with cases of degrees of coherence from the slight attachment of the petals of a Flax or Woodsorrel to the complete union of these parts in a Convolvulus or an Erica, from the connection of the petals at the base only in some cases, to its reaching the very tip in others, and we may have seen a little starvation restore a Bellflower or Convolvulus to five separice petals. It is necessary, to be able to express what happens in precise and accurate language, and as the terms monosepalous, monopetalous, af- firm what is well known not to be true, and are fitted to obscure the ideas of students, whilst DeCandolle's terms, gamosepalous, gamope- talotis, are figurative and too long, and have met with liMle aceept- ance, I take this opportunity of -proposing terms long used by me, as a teacher, which seem fully to supply what is needed without being liable to objection. Let tlie coherent parts be called synsepalotu, ki .« I Wm I ON CHORI8I8. tynpetaloui, and if you please, synandroua, tynearpeUnus, whilst aepa> ration may be expressed by apoaepalous, apopelaloua, jj-c. Adherence •rises from pressure of the circles on each other, or expansion of the torus or receptacle, so as to adhere sometimes outward on the lower part of the calyx, sometimes inward on the combined carpels, some- times in connection with both, so as to place the fruit below the other circles of the flower and produce the epigynose structure— it readily explains many phenomena of common occurrence in flowers. Regularity and irregularity of flowers depend entirely on the equal or unequal distribution of nutrinieut to the parts of the successire circles, the causes of which difllrences are often undiscernible, though the fact is certain. Sometimes the more developed parts are in all the circles on the same side of the flower ; in other cases the opposite sides are enlarged alternately. In other instances the irregularity is produced bv an opposite pair being enlarged in each circle (where the whole number of parts is evenj, or by this arrangement being alternated in the successive circles. It must be evident how many modifications of flowers are explained by these considerations. The primary law respecting number is found in the tendency to the number three in the circles of mono-coty ledonous plants, and to five in those of dicotyledonous plants. The first is an ultimate law of the organization of plants abundantly established by fact, but hardly capa- ble of being connected, so far as we can at present see, with anything else we know of their nature. It may be doubted whether the second is not connected with the first in as much as one cotyledon or primor dial leaf is found to imply a circle of three parts, two would therefore be expected to produce six, but this supposes the combination into one of two circles of three. Now we have other examples of this sort of combination of circles of parts exhibited to us by certain anomalous flowers, in sufticient number and variety of cases to suggest a sort of rule as to what is likely to happen, and from them we infer that in ordinary cases one part would be lost in the union. That under con- fiiderable pressure a part would he lost at each point of junction or two in the combined circle, whilst very close position, with circumstances unfavourable to development, such as give us occasional examples of two and oue part in a monocotyledonous plant might occasion any of the lower numbers to occur in a dicotyledon. I found the exj)lanation here given of the prevailing number of dicotyledonous plants on the careful examination of a considerable number of those monstrosities, not • V ,li ON CHOK18IS. 7 of very uncommon occurrence, in which two flowers nrc combined into one from their origin, owiiiK to their buds having been adjacent. I can now distinctly recall examples in two or three species of Iris, and in at least three speciesofOenothera, my cultivation at one period of numerous species of those genera affording me (he opportunity of observing the anomalies to which they are liable. I had various instances of circles of five in the monster Iris and of seven in the Oenothera— one instance of four in the Iris in a single circle and one of only three, the exterior circles having five, and the tube showing sufficient marks of the union. In the Oenotheras observed, which embraced several species, there were uniformly seven parts in each circle, that is, seven sepals, seven petals, fourteen stamens and seven carpels. I gave some account of these monstrosities to the Linnoean Society in 1 839, and it has since occurred to me that they establish a law respecting the combination of circles of growing parts, which may explain the tendency to the number five In Dicotyledonous plants, since, when growth is carried on from a single cotyledon, we find the number three in the circles, and where there «re two cotyledons we might expect the circle to be double, but the fact of the loss of at least one part in combinations of two circles on the same plane shows why the number five takes the place of six. The liability of the natural numbers, five in Dicotyledonous and three in Monocotyledonous, to be reduced by mere pressure or by irregu- larity, is obvious from what has been already said. We find by obser- vation that the number of parts in the successive circles of the flower is usually equal, but that the inner circle, being exposed to greater pressure, is apt to have fewer than the others — three and two carpels being very common in Dicotyledonous plants. In some structures the numbers in the different circles do not at all correspond, but tiiis, which is characteristic of particular families, is less common, and its origin is one of the most obscure and dubious points in the theory of the flower. When parts are absent either from pressure or irregu- larity, we must remember that the fact is due to a special cause of abortion, not to the total absence of the i)art from the structure, and consequently that circumstances may occur from more abundant or equally distributed nourishment, which may in anomalous examples restore the missing part. Such examples are, nideed, almost needed to confirm our judgment as to the causes of the ordinary absence of these parts, and have therefore great interest for the philosophical botanist. In the natural family of the Onagraceze, to which the genera Fuchsia f I 8 ON CHORI8II. and Oenothera belong, the reduction by pressure of the natural num- ber to four instead of five, and sometimes to a smaller number, is char- acteristic, but it is by no means uncommon to observe the restoratioi of the fifth part ia both Fuchaias and Oenotheras under high culture and, when it occurs at all, it takes place uniformly through all tha circles. I have seen various examples in both genera. In the great order Fabaceie, the Leguminous plants, a single carpel from abortion through irregularity of the rest of the circle is characteristic, but I have often met with kidney beans with two opposite carpels united by their edges so as to remind us of the maple fruit, and ia Acer Pseudo- platanus, the Sycamore, I have found, instead of the usual pair of earpels, a complete circle. We are thus forced to admit that tha parts deficient in particular structures are absent through abortion, but were rudimeatally present in the bud, capable under favourable inlluences of being developed. In fact the number five is very common in the exterior circles of Dicotyledonous plants, less so ia the gyncecium, though often occur- ring there nlao; four is often produced both by pressure and by irregularity, three is occasionally found, and two rather more fre- quently, whilst in cases of the least amount of development, where the circles are reduced to two, or even one, a single organ in that circle is all that appears. In monocotyledonous j)lants the number three, and, from additional circles, its multiplies, is somewhat more constant, but abortion or degeneracy of organs from irregularity, is found through- out the Musal and Orchidal alliances and in grasses ; and other irrei'U- larities of number occur. Our general laws of Floral structure, once understood, leave little difficulty in recognizing the proper explanation of the facts as they fall under our notice. Having now shortly reviewed those principles which m;>y be regarded as admitted among those botanists who apply themselves to the theo- retical relations of the flower and its organs, tracing what is common and accounting for what is varied in the different structures, and hav- ing ventured to add one or two suggestions for improving these views or the mode of expressing them, we are prepared to estimate the evi- dence for any additional principle, where we have to judge whether the phenomena are susceptible of good explanation by the aid of those already established, or really require some new generalization for the correct expression of what occurs, and the perception of its true rela" tions with other facts — and then whether the proposed principle agrees ON f '^CRIBIt. « with and htrmonisM all the facta ao aa to be received aa what we call a geod explanation of them. The kind of facta which thon»i» under- takea to explain are cases in which the avmiretry of the flower as commonly understood would suggest the expectation of one organ hot we actually find two or more, and these in an unusual d-gree of proximity; cases in which the multitude of apparently distinct organs produced in close proximity seems inconsistent with the supposition of their belonging to succewive circles ; those in which a number far exceeding the natural number seems to be found distinctly in one cir- cle, and those in which a number of similar organs are combined at their base in clusters, the number of clusters corresponding to what might have been expected to be the number of organs. All these are represented as being capable of explanation by collateral chorisis or the ■ubdivision laterally of one organ into e. number of organs. There is alf a different class of facts, such as the occurrence of organs arising ou the face of other organs and opposite to them : sometimes of lines of opposite organs, which bping supposed inconsistent with other principles of structure, are explained as cases of transvenc chorisis, or the division of a single organ into folds like the splitting of a card into two or even many similar or related organs. It cannot be denied that the cases to which chorisis has been applied as an explanation are attended with some difficulty, and that some of them are even incapa- ble of plausible explanation by previously established principles- Some of them, however, appear to me quite consistent with those prin- ciples, as I shall endeavour to show when examining some alleged examples, and although it cannot reasonably be affirmed that such an operation as chorisis is inconceivable as arising from the nature of the organs of the flower, and it seems even to be sanctioned by some facts, yet I find myself obliged at least to limit its application within much narrower bounds than some able botanists have assigned to it. My rea- Bona will be best given in an examination of the particular cases brought forward at least a sufficient number of them to justify a general opinion on the subject. I shall take the examples given by Dr. Gray, who adopts fully the theory of chorisis in his valuable work, the Botanical Text Book. pp. 250-2.55, having reference also to his remarks in •• The genera of the United States Flora, illustrated.'* Dr. Gray's first ex- ample of collateral chorisis, on which he is disposed greatly to rely, is found in the Tetradynamous stamens of the natural family Bramca- ee