May 20, 1898.] 



SCIENCE. 



699 



theory be rejected it must not be forgotten 

 . how many valuable facts are due to his 

 activity in this field. The effects produced 

 by the chemical and physical state of the 

 soil upon transpiration, the checking action 

 of salt solutions, low temperatures, etc., 

 were well established ; the 'Lithium Method' 

 was used for measuring the rate of the trans- 

 piration current ; and the profound and far- 

 reaching importance of transpiration for 

 the life of most plants was demonstrated. 



A further laborious and protracted series 

 of experiments dealt with the phenomena 

 of growth and of movements produced by 

 stimuli. Among the more notable of these 

 are the construction of the first auxanom- 

 eter, the graphic description of his observa- 

 tions, and the recognition of the grand 

 period of growth. His investigations into 

 the growth of the main and side roots 

 first proved convincingly the factors which 

 condition the regular extension of the root 

 system in the ground, and established the 

 distribution of growth in roots, as well as 

 the correlation between main and side 

 roots. A number of isolated observations 

 are also to be found in this exhaustive 

 treatise. Sachs' clear, perspicuous style 

 renders it a pleasure to read any of his 

 essays, even when he is compelled to enter 

 minutely into detail. 



The phenomenon of ' Hydrotropismus ' 

 (the name originated with Sachs) had al- 

 ready been occasionally investigated, but 

 Sachs showed it to be due to irritability, 

 demonstrated its importance and facilitated 

 the examination of it by a simple appara- 

 tus. The ' Hangende Sieb ' (hanging sieve) 

 is now to be found, like the auxanometer 

 and the klinostat, in every botanical labora- 

 tory. 



The ' Tropisms ' (Heliotropism, Geotro- 

 pism, etc.) made large demands upon his 

 time and attention. When under Hof- 

 meister's influence, as regards experimental 

 physiology, he inclined to an external, me- 



chanical conception of these, but abandoned 

 this later. His own words best denote his 

 standpoint: "I, too, should have nothing 

 to say against the term ' Lebenskraft ' 

 (vital force), and have indicated as much 

 from time to time in my 'History of Botany,' 

 but the word has been spoilt and rendered 

 nugatory by misuse. I say, therefore, to 

 denote my conception of the organic world, 

 that the province of true physiology begins 

 where that of mechanics, physics and 

 chemistry of organisms ends. Indeed, I 

 go farther and maintain that the time will 

 come when in physiology will be found the 

 ultimate basis (what Goethe speaks of as 

 'die Miitter') of all natural sciences." 

 There is no need to say that this vitalistic 

 view did not prevent him fi-om working out 

 with the deepest interest the phenomena of 

 growth-curvatures. He also established 

 the phenomenon known as ' after-effects,' 

 and contributed many other valuable iso- 

 lated experiments. 



If he attached great importance to theo- 

 ries, he was fully conscious of their transi- 

 tory nature ; and I might mention, as an 

 example of this, that in his later years he 

 did not lay so much stress upon his theory 

 of Heliotropism. There will be more to 

 say about this when reference is made to 

 his treatise on orthotropic and plagiotropic 

 organs. 



In the meanwhile attention must be di- 

 rected to the essays upon the connection 

 between cell- formation and growth, which 

 in my opinion belong to his most brilliant 

 achievements. As a result of Nageli's re- 

 searches on the apical cell, numerous botan- 

 ical works had arisen dealing with the laws 

 of cell-division. It was this tendency, ex- 

 aggerated until it was justly dubbed ' Zell- 

 fangei'ei,' that led men to neglect plants and 

 organs as a whole for the mere cells, and 

 to take it as granted that growth is deter- 

 mined by the manner and method of cell- 

 division, much as the shape of a building 



