VITALITY AND GERMINATION OF SEEDS. 193 



oxygenated areas than in ones deficient in oxygen is 

 well known, and it appears that the primary radicle more 

 especially and to a lesser extent the secondary roots 

 possess the power of seeking out within given limits and 

 under appropriate conditions of stimulation the better 

 oxygenated areas of soil and turning to them in preference 

 to areas deficient in oxygen. 



Since the above was written I have found that H. 

 Molisch (Ueber die Ablenkung der Wurzehn von ihrer 

 normalen Wachsthumsrichtung durch Gase. Ber. D. Bot. 

 Gesell., 1884, II., p. 160) has already described this 

 special form of irritability as occurring in the roots of 

 Zea, Cucurbita and Pisum, and has given it the name of 

 " aerotropismus." The term " oxytropismus " seems to 

 me to be better than " aerotropismus," but the latter has 

 of course priority. The experiments here described 

 support in all essentials the conclusions drawn by Molisch. 

 The curvatures, however, which he found could be 

 induced in many roots by the action of various poisonous 

 gases are probably to be regarded as Traumotropic in 

 nature and do not seem to have any connection with the 

 true " oxy tropic " irritability of the root tip. 



