168 SCIENCE PROGRESS. 



side roots. A number of isolated observations are also to 

 be found in this exhaustive treatise. Sachs' clear, perspicu- 

 ous style renders it a pleasure to read any of his essays, 

 even when he is compelled to enter minutely into detail. 



The phenomenon of " Hydrotropisms ' : (the name 

 originated with Sachs) had already been occasionally in- 

 vestigated, but Sachs showed it to be due to irritability, 

 demonstrated its importance and facilitated the examina- 

 tion of it by a simple apparatus. The " Hangende Sieb " 

 (hanging sieve) is now to be found, like the auxanometer 

 and the klinostat, in every botanical laboratory. 



The " Tropisms ' (Heliotropism, Geotropism, etc.) 

 made large demands upon his time and attention. When 

 under Hofmeister's influence, as regards experimental 

 physiology, he inclined to an external, mechanical con- 

 ception 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 Mutter") of all natural sciences. There is no 

 need to say that this vitalistic view did not prevent him 

 from 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 isolated experiments. 



If he attached great importance to theories, he was 

 fully conscious of their transitory 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 directed to the 



