292 



SCIENCE. 



[N. S. Vol. XXIII. No. 582. 



phological oue. Since the appearance of 

 the 'Origin of Species,' we have had de- 

 veloped, particularly in the realm of plants, 

 the conceptions of the special science of 

 ecology or epharmony. The rapid growth 

 of this science has led to the clear realiza- 

 tion of how remarkably the external form 

 of plants may be assimilated by similar 

 modes of life. Later still is the appear- 

 ance in a pronounced form of the doctrine 

 of mutational or saltatory evolution of 

 species. The establishment of these two 

 new disciplines, both having tirm scientific 

 foundations, has tended to weaken the hold 

 of morphology on the scientific mind. For 

 if the form of plants may be instantly and 

 profoundly modified by the still occult 

 process of mutation, or more sloM'ly but not 

 less surely by the more obvious influence 

 of external conditions, then it is not un- 

 natural that less importance should be at- 

 tached to form and structure, which are 

 the subject matter of morphology. And 

 yet the doctrine of descent, the great out- 

 standing generalization of the biological 

 sciences, which few of us probably expect 

 to see overthrown, is bound up with the in- 

 tegrity of the science of morphology. The 

 doctrine of descent or phylogeny depends 

 for its validity on the correctness of the 

 inference that marked similarities of struc- 

 ture indicate a more or less close degree of 

 relationship. In the existing situation, the 

 new studies of ecology and mutation, still 

 in the first gloss of their novelty, tend to 

 outshine the older yet not less finnly 

 founded science of morphology, which 

 through lapse of time has suffered as it 

 were a certain degree of surface tarnish. 

 Newer aspects of morphology are, however, 

 coming to light at the present time, which 

 promise to restore to the subject all its 

 former brilliancy. It is my intention this 

 morning to give some brief account of 

 these new developments. 



A prevailing principle in the past in 



morphology has been to trace back organs 

 or tissue-systems to a similar mode of 

 origin from the growing point or young 

 organ and hence to infer their morpholog- 

 ical equivalence. Thus, for example, the 

 morphological essence of a sporangium has 

 been thought to exist in the possibility of 

 deriving its sporogenous tissue from a 

 clearly defined and early developed pri- 

 mordium known as the archesporium. 

 Similarly the morphological value of the 

 central cylinder or fibrovascular system of 

 the higher plants is thought by many mor- 

 phologists to depend on its origin at the 

 growing-point of the organ, root, stem or 

 leaf, from that so-called primary meristem, 

 known as the plerome. In the c£ise of the 

 sporangium, the illuminating researches of 

 Professor Bower have made it clear that 

 not only may spore-producing cells arise 

 outside the so-called archesporium, as in 

 Equisetum, but also sterile or asporogen- 

 ous tissues may originate from mother cells 

 apparently destined to form spores, as in 

 Tmesipteris and Isoetes. In the case of the 

 sporangium, it is accordingly clear that its 

 fundamental characteristic is that it pro- 

 duces spores and not that its sporogenous 

 tissue originates from an archesporium. 

 There can be no doubt whatever that in 

 the vascular plants a spore is to be re- 

 garded as morphologically a spore, whether 

 its mother cell comes from the so-called 

 archesporial complex or not. In the case 

 of the central cylinder of stele, the clash 

 of many minds has not yet resulted in a 

 similar general clarity of reasoning. If 

 we, for example, choose the case of the cen- 

 tral cylinder of the root in the Angio- 

 sperms, which the recent very exact re- 

 searches of Schoute show to be derived 

 definitely and entirely from the plerome 

 strand of the growing-point, we have a 

 result which is in so far satisfactory from 

 the standpoint of the older morphology. 

 If we, however, proceed to the consideration 



