THE PHYLOGENY OF THE SOUL. 161 



had none. However, an unprejudiced comparison of 

 the irritability and movements of various higher 

 plants and lower animals convinced many observers, 

 even at the beginning of the century, that there must 

 be a " soul " on both sides. At a later date Fechner, 

 Leitgeb, and others, strongly contended for the plant- 

 soul. But a profounder knowledge of the subject was 

 obtained when the similarity of the elementary struc- 

 ture of the plant and of the animal was proved by the 

 cellular theory, and especially when the similarity of 

 conduct of the active living protoplasm in both was 

 shown in the plasma-theory of Max Schultze (1859). 

 Modern comparative physiology has shown that the 

 physiological attitude towards various stimuli (light, 

 heat, electricity, gravity, friction, chemical action, 

 etc.) of the " sensitive" portions of many plants and 

 animals is exactly the same, and that the reflex 

 movements which the stimuli elicit take place in 

 precisely the same manner on both sides. Hence, if 

 it was necessary to attribute this activity to a " soul " 

 in the lower, nerveless metazoa (sponges, polyps, etc.), 

 it was also necessary in the case of many (if not all) 

 metaphyta, at least in the very sensitive mimosa, the 

 "fly-traps" {dioncea and drosera), and the numerous 

 kinds of climbing plants. 



It is true that modern vegetal physiology has given 

 a purely physical explanation of many of these stimu- 

 lated movements, or tropisms, by special features 

 of growth, variations of pressure, etc. Yet these 

 mechanical causes are neither more nor less psycho- 

 physical than the similar " reflex movements " of the 

 sponges, polyps, and other nerveless metazoa, even 

 though their mechanism is entirely different. The 

 character of the tissue-soul reveals itself in the same 



