700 



SCIENCE. 



[N. S. Vol. VII. No. 177. 



is determined by the way the building- 

 stones are laid one upon another. 



Hofineister's brilliant, though hardly 

 well-grounded, opposition had but little suc- 

 cess ; only a few botanists took any notice 

 of it. It was Sachs who, in his usual clear 

 manner and by the aid of simple contriv- 

 ances, first explained the relations between 

 cell-disposition and growth. In his opinion 

 the latter is the determining factor, the ar- 

 rangement of cells depending upon growth. 

 This explained why, for instance, cross-sec- 

 tions through cylindrical masses of cells in 

 plants belonging to widely separated groups 

 may present the same appearance of cell- 

 arrangement as a developing alga or a hair 

 of a dicotyledon. The introduction of the 

 terms ' anticlinal ' and ' periclinal ' made a 

 brief, striking bird's-eye view of the matter 

 possible, and facilitated further study of the 

 changes in cell-disposition occurring during 

 growth. A large group of facts was brought 

 together under a common heading, and not 

 only was the way made smooth for further 

 investigations into the causes of the arrange- 

 ment of cells, but an important point of 

 departure was also made for experiments 

 on the evolution of organs which do not 

 possess an apical cell. 



The changes which had gradually taken 

 place in the cell theory have led to an en- 

 tire alteration in its original meaning. This 

 prompted Sachs, who always felt the need 

 of clear and consequently historically cor- 

 rect conceptions, to introduce the definition 

 ' EnergicL' In my opinion he therebj^ ren- 

 dered good service to science. It was a 

 great satisfaction to him that his achieve- 

 ments found favor with the most eminent 

 histologists (Kupffer, for instance), and this 

 consoled him for the fact that the botanists, 

 now as on other occasions, instead of test- 

 ing the innovation in its general applica- 

 tion, sought only too zealously for instances 

 in which it did not apply. But the time will 

 surely come when it will be deemed absurd 



to describe a Caulerpa, for instance, as a 

 ' unicellular ' plant, and it fell to Sachs to 

 fit scientific nomenclature to recent ad- 

 vances in knowledge. It was self-evident 

 to him that definitions are only a means 

 towards generalization and that they have 

 absolutely no validity in themselves. 



The essay upon orthotropic and plagio- 

 tropic plant-parts takes us into a region 

 that lay nearest to Sachs' heart during the 

 last years of his life, namely, that of phys- 

 iological or causative morphology. In this 

 treatise he deals with the connection be- 

 tween the structure (in the widest sense of 

 the word) and the direction of the organs. 

 The definitions ' orthotropic ' and ' plagio- 

 tropic ' were introduced, and referred more 

 particularly to the dorsiventral structures 

 that had long been neglected under the 

 supremacy of the ' spiral theory.' He does 

 not merely treat of the purely structural 

 conditions, but of the causative relations 

 between orthotropic growth and dorsiven- 

 tral structure. Sachs would, I believe, have 

 altered later his theoretical conclusions 

 upon plagiotropism ; they are based upon 

 ideas which he no longer held, as we may 

 see in the text, to be as thoroughly war- 

 ranted as formerly. But putting aside these 

 points, about which opinions still differ, we 

 find ideas in this essay that are still work- 

 ing with considerable effect in morphology. 



As a morphologist Sachs' activity dis- 

 played itself in one direction by some special 

 studies that date fi'om his earlier years, in 

 another by his text-books, and again by his 

 final general essays. 



His two treatises, on Collema* and Cru- 

 cibulum, show him at work in the region of 

 cryptogams. It was he who in his ' Text- 

 book ' defended Schwendener's Lichen 



* In this essay he approached very closely to the 

 later lichen theory when he said that it looked as if 

 a parasitical fungus had established itself in the nos- 

 toc ; he believed that the nostoc-heterooysts might 

 develop into a myoellium. 



