1026 REPORT— 1898. 



the next phase of our study, to which it ^ave its character. And now the need 

 arose for observing development ; tbis was initiated by Schleiden, and carried to a 

 triumphant climax hj Hofmeister. Passing from the hands of these pre-Darwinian 

 to those of post-Darwinian writers, the comparisons, while remaining virtually the 

 same, received a new significance. Observers now pushed their inquiries into the 

 details of anatomical structure and development, and in many cases attached an 

 importance beyond what is justifiable to minute similarities or differences of cell- 

 cleavage. Thus what might be called ' cellular morphology ' became a feature of 

 the period. It has, however, been in a measure discredited by the excessive zeal 

 of some of its votaries, who drew large conclusions from slight facts ; a salient 

 example of this is furnished by studies concerning segmentation of the ovum. 

 But we must not assume that because it has been pursued indiscreetly the study 

 of segmentation is effete ; there is still scope for valuable observation, which will 

 hear a reasonable burden of argument ; though conclusions from such a source must 

 be compared with those derived from other data, and a due estimate of them must 

 be made accordingly. 



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

 view to ascertaining the effect of external agencies in determining form, and the 

 limits of variability under varied circumstances. Development of itself shows 

 only how a part originates ; it does not demonstrate what it is, nor what it may 

 become under special conditions. This new and growing phase of experimental 

 morphology, together with comparison from the point of view of descent, now 

 tends to supersede the formal morphology of the second period, which in many 

 minds implied or assumed ideal types or creative plans. It has become a general 

 Tiew that the facts of morphology are but the stereotyped facts of physiology, 

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

 third 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. We watch 

 Nature's compositor at work, but we also ascertain that the plate itself, after it is 

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



These three phases of morphological inquiry have naturally overlapped one 

 another ; we recognise, however, that first description, then formal comparison, 

 and now experiment, have been the leading features in morphological investigation 

 during these successive periods. 



Homology. 



The ideal aimed at in the study of the morphology of plants is to trace their 

 real relationships and mode of origin, on the basis of the widest observation — in 

 short, to reconstruct the evolutionary tree. In order to make comparison po.ssible, 

 or at least manageable, a terminology is necessary, and this not only of the plants 

 themselves, but also of their parts. We may for the moment leave on one side 

 that summing up of morphological opinion represented by the systematic arrange- 

 ment of plants in a taxonomic system. I propose to-day to discuss not the classifi- 

 cation of plants, but the classification of the parts of plants, their grouping accord- 

 ing to their homologi/. And here I use a word which is probably explained to 

 every class of elementary students ; it is one of those terms a meaning of which is 

 indeed revealed to the babes of the science, while those who teach are not at one 

 as to its definition. We need not enter now into the various opinions which have 

 heen held on this point, nor need we make any antiquarian research into the 

 introduction or early use of the word homolo(jy ; it will suflSce to state that it was 

 already firmly established in the science before views as to descent gave it any 

 intelligible meaning. We speak of the homologies recognised by Hofmeister, but 

 it should be remembered that their great discoverer did not put an evolutionary 

 interpretation upon them. Sachs points out in his history how ' the theory of 

 descent had only to accept what genetic morphology had already brought to view.* 

 Nevertheless, much remained ingrained in the very texture of the science which 

 was incompatible with evolutionary thought. This was so even in the te.xt-book , 

 of Sachs itself. The categories of root, stem, leaf, and hah* are there laid down, and 



