The Living Machine 



311 



complete leaf than in one with a leaf which has been partly 

 cut awa3^ "What has been demonstrated in this case explains 

 probably also why the apex of many plants when put into 

 a horizontal position grows upward, and why certain roots 

 under similar conditions grow downward. It disposes also 

 in all probability of the suggestion that the apex of a posi- 

 tively geotropic root has 'brain functions.' It is chemical 

 mass action and not 'brain functions' which are needed to 

 produce the changes in growth underlying geotropic curva- 

 ture. "^ 



Such an explanation however is difficult to apply to many 



Eelative Amount of Bending 

 Due to unequal growth in stems with and those without leaves. 

 Loeb, "Forced Movements, Tropisms and Animal Conduct." 

 By permission of J. B. Mppincott Company. 



From 



of the reactions of a Stentor or a Paramoecium. AVhile the 

 latter animal reacts to an electric current by a cjifference in 

 the beat of the cilia on the two sides, and the animal is thus 

 turned so as to swim with the current, by a process seem- 

 ingly as mechanical as that of turning a boat; in other 

 cases, as when running into a salt solution, the behavior of 

 Paramoecium is not so simply explained, for in this circum- 

 stance it always turns in the same direction, regardless of 

 the angle at which it meets the salt current, and even though 



* Loeb, "Forced Movements, Tropisms and Animal Conduct," i)p. 

 121-2. By permission of J. B. Lippincott Company. 



