602 



GARDENERS" MAGAZINE. 



September i? , 



Homology of Plants. 



" By Professor F. O. Bower, D.Sc./F.R.S. 



The following is the text of the important address delivered by Professor 

 F. O. Bower, D.Sc, F.R.S., president of the Botanical Section of the 

 British Association, at the opening meeting of that section :— 



Shortly before we met last year, in the hospitable Dominion of 

 Canada two biologists, whose work relates to the questions I propose to 

 discuss to-day, passed away. In both cases their services to science had 

 received honourable recognition in this country. Johannes Japetus 

 Smith Steenstrup, who had been for more than thirty years a foreign 

 member of the Royal Society, died June 20, 1897, at the advanced age of 

 eighty-four ; Julius von Sachs, also a foreign member of the Royal 

 Society, died May 29, 1897, aged sixty-five. 



The former of these, a zoologist, was probably best known in this 

 country for his work on " Alternation of Generations," a translation of 

 which was published by the Ray Society in 1845. The title-page 

 describes the phenomenon as " a peculiar form of fostering the young in 

 the lower classes of animals." Botanists should remember that this term 

 "alternation," which they often use in a sense peculiarly their own, was 

 originally applied to the course of development in certain animals, by 

 Chamisso in 1819. The first general statement of the subject from the 

 zoological side was by Steenstrup in the work already named ; even 

 there no mention is made of such phenomena in plants, until the con- 

 cluding paragraph, where there is an allusion in very general terms to 

 the course of events in the life of seed-bearing plants. But when we 

 remember that it was only in 1848 that Suminski discovered the 

 antheridia and archegonia borne upon the prothallus of a fern, we see 

 plainly that Steenstrup could not have used the term "alternation" in 

 the sense in which it is now generally applied to plants. The interest 

 for us as botanists will therefore be that Steenstrup suggested in his work 

 on alternation in animals how in the life of plants successive phases 

 exist, and that these are comparable to those which he described in many 



animals. 



Work of St. Julius Von Sachs. 



VIZ. 



The work of Sachs, on the other hand, has influenced every one of us. 

 Some, including myself, have had the great advantage of his direct 

 personal guidance ; all must have derived pleasure as well as profit from 

 his writings. I shall not here attempt any general summary of the 

 achievements of this great man, for that has been done efficiently by the 

 scientific Press at large. I shall merely allude to one feature of his work, 

 the style of its presentment to the reader. He was always clear, 

 usually concise. He was, in addition to his power as an investigator, a 

 master with the pencil, as well as with the pen. It was this combination 

 of qualities which made him the great text-book writer of his time. Never 

 perhaps has a volume more fairly reflected the position of a science at 

 the moment of its publication than did that of Sachs. It resembles 

 the work of a snap-shot camera, and, like any instantaneous photograph 

 of life in motion, it has fixed and perpetuated awkward positions. The 

 morphological system of the time was stiff and unpromising ; the text- 

 book accurately depicted this, but it did not suggest or anticipate future 

 developments ; it did not bear the softened image of a longer exposure ; 

 it presents to us the angular attitude of a moment. 



The powers of Sachs as a writer found their best scope in his 

 " History of Botany," a work which will always retain its value as a 

 masterly exposition of the results of very wide reading, arranged with a 

 literary skill which is, unfortunately, rare among scientific men. I lay 

 stress upon this power of Sachs as a writer, apart from his record as an 

 investigator, because he was strong where so many of us are weak. The 

 truth is that little effort is made by men of science to use a concise and 

 transparent style ; for the most part we write by the aid of such instincts 

 as Nature has given us ; few cultivate composition. But it should, I think, 

 be impressed upon the young aspirant that, when he writes, it is one of 

 his first duties to consider his readers' convenience ; he must use all 

 endeavours to convey forcibly the result of his inquiry, but to make the 

 least possible demand upon the patience of his readers. 



Three Phases of Morphological Study. 



It will be in your memory that the address of last year's Sectional 

 President was largely devoted to branches of our science which touch 

 the material and economic interests of man. It was pointed out to us 

 how certain fungal diseases diminish agricultural profits to an extent 

 which may be ^estimated in millions of pounds yearly. Beneficent 

 microbes were also mentioned, such as those which govern the aroma 

 and maturing of butter and cheese ; these and many others, the study of 



lines referring to the legendary organism 



suggested by the peculiar f„ rm of aS& (i ffl«|U« pU», 



Cradled in snow and fann'd by arctic * ~ 

 Shines gentle Barometz, thy golden hair 

 Rooted in earth each cloven" hoof Ses £ds 

 And round and round her flexile neck she bend, . 

 Crops the grey cora l moss , and hoary t hyme 1 

 Or laps with rosy tongue the meltingrime 1 



And now the need arose for observing- devplnnm*«f 7u- ^racfct 

 by Schleiden, and earned to a tri^fS^rf*^ 

 from the hands of these ^re-Darwinian to those of 

 writers, the comparisons, while remaining virtually the same, S 

 new significance. Observers now pushed their inquiries into thTdSj 

 of anatomical structure and development, and in many cases attaclSt 

 importance beyond what is justifiable to minute similarities or differ** 

 of cell-cleavage. Thus what might be called « cellular roorpholoinrS 

 came a feature of the period It has, however, been in a measure £ 

 credited by the excessive zeal of some of its votaries, who drew large cot 

 elusions from slight facts ; a salient example of this is furnished by studio 

 concerning segmentation of the ovum. But we must not assume tfat 



because it has been pursued indiscreetly, the study of segmentation « 

 effete. 



Morphology has lately passed to a third stage— that of experiment- 

 with a view of ascertaining the effect of external agencies in determine 

 form, and the limits of variability under varied circumstances. Develop- 

 ment of itself shows only how a part originates ; it does not demonstrti 

 what it is, nor what it may become under special conditions. This net 

 and growing phase of experimental morphology, together with compuv 

 son from the point of view of descent, now tends to supersede the fonml 

 morphology of the second period, which in many minds implied or 

 assumed ideal types or creative plans. It has become a general viewthat At 

 facts of morphology are but the stereotyped facts of physiology, fora 

 being determined by function, but under the check of heredity. This thai 

 experimental phase of the study of plant-form, is directed, as it were, to 



the very setting of the types, before the stereotype plate is cast Wew 

 Nature's compositor at work, but we also ascertain that the plate \wM, 

 after it is cast, is much more plastic than some of us had thought 

 These three phases of morphological inquiry have naturally 



hipped one another ; we recognise, however, that first description, thet 



formal comparison, and now experiment, have been the leading featurti 

 in morphological investigation during these successive periods. 



Homology. 



The ideal aimed at in the study of the morphology of plants is toOTtt 

 their real relationships and mode of origin, on the basis of the JJ*J 

 observation in short, to reconstruct the evolutionary tree inotoerw 

 make comparison possible, or at least manageable, a termino '°^^.' 

 necessary, and this not only of the plants themselves, but also ot inrj 

 parts. We may for the moment leave on one side that summing up 

 morphological opinion represented by the systematic » r ™ n £ m ?" . 

 plants in a taxonomic system. I propose to-day to discuss not f » 

 cation of plant,, but the classification of the parts of plantsjne r jt ~r 

 ing according to their homology. And here I use a word wwca ^ 

 bably explained to every class of elementary students; u is ^ 

 terms a meaning of which is indeed revealed to the banes 01 mim 

 while those who teach are not at one as to its dehn ' ll °"j on thij pa* 

 enter now into the various opinions which have ,)een . inlr0 ductioo of 

 nor need we make any antiquarian research into ^ ^ 

 early use of the word homology; it will suffice to staw : u. 

 firmly established in the science before views as tones * _ , 

 intelligible meaning. We speak of the homolo pe» 

 Hofmeister, but it should be remembered that _ tneir h ^ p^tso* a 

 not put an evolutionary interpretation upon t nem - t wnat 

 his history how " the theory of descent had [only to , ac 

 morphology had already brought to view M serine ^ «*i 

 ingrained in the very texture of the science wj> ch * ^ 0 f Sacks ** 

 evolutionary thought. This was so even m trie re * bi<| down . «f 

 The categories of root, stem, leaf, and hair are 1 ^ ^ k om *g m 

 the parts classed under these several heads weie , _, inn wc:! 



act ers ^^Tve position;!" -5 

 aside, the definitions relating to *P^?^J\$L the result that 9» 



In their definition all those characters-which refer toju^non^ ^ 



!gir 



parts were described as bearing a varying m^^^ia were fg 



ductive organs were grouped with the rest, 



value Bet 



which lies properly within the province of botany, affect not only the purely formal morphology is now dead ; it 10,, {» t ; ce has stta»r!V 

 health, but, at the most varied points, the prosperity of mankind. belief in evolutionary views, but their _ .J^nition of $P^^ 



It is unnecessary for me to dwell further upon these points or to urge 

 again the utilitarian argument for the proper support of botany. 



I Oronnse. nn tho <-,<-!-> V.^„.-l lj» ■■;*«» vnur nttpntinn to the 



argument for the proper si 

 propose, on the other hand, to invite your 

 morphology of plants. This is a department of science pure and simple. 

 The results which it brings have not, and cannot be expected to have, 

 any money value in the markets of the world. The present time is one 

 of unusual bustle and change in morphology, consequent upon the 

 discovery of new facts and the introduction of new methods. The 

 development of the study may be divided into three periods, we ourselves 

 standing upon the threshold of the third. 



in tvuiuuuiiaiy ncns, u«<- , recognition «• -r 



The first step towards emancipation was the r ^ s nd Strasburg*'- *T 

 parts sui generis. Eichler, agreeing with , Braun ^an ^ 

 it " highly probable according to h % theory ^hologicalJJJ 

 structure as the ovule has universally cne j> ment that 

 It remained for Goebel to make the general n0 t the 



stand in a category by themselves, and are ^ ^ ^ thatOKJ- 

 modification of any vegetative part. 11 aauesuoow J^gt§t 



genetic factor was 'first asserted as bearms on m t nolottgj ^j 

 in the morphology of plants. Adherents or ^^ye^i 



The earliest phase was that accepted the direct results of investigation , position «as 



. . • 1 J il 1 1 i 1 „f tViem : DUl U*» r , p^r^in S 



of description and delineation of what niieht be observed of the mature and control the interpretation of them ; but j 

 torm of plants ; this includes the work of the herbalists and of the till more than twenty years after the P" 15 ^ deiC , 



J™eThT\K matlStS ' l - hus fomished the basis for classification. It is 

 mad e but tWnf? descr !P tio n was enriched at times by comparisons 

 SkSs T?lte.°^i«*: > capricious form, as is shown by the many 



to descent ba« u y .ve ^ 



creasi 



tuuous allusions which <ttil1 -~ r " *r 



Darwin satiric • • s . urV5v e m the nomenclature, 

 writers in nis «' 1 m - 'W^ive comparisons indulged in uy cany 



m his Loves of the Plants » ; an instance of this is seen in his 



Erasmus 

 in by early 



Species." Since then, however, views nlor pholog)*. , --frd « 



ngly important place in the P rov, "^ n ° 0 f allied ^£0** 

 sent moment a far reaching compa riso^ u ^ handJ m 

 experiment, is the most potent instrunoen 



l0giSt ( To te continued. } 



