90 THE PSYCHIC LIFE 



of the Hepaticae. The author concludes from this, 

 that the substance operating in these two cases can be 

 little diffused throughout the vegetable kingdom. 



For the spermatozoids of the Funaria hygrometrica 

 (Confervae), the operative substance is cane-sugar. 

 No other attracts them. The spermatozoids remain 

 unaffected even by substances bearing the closest anal- 

 ogies with cane-sugar. We will cite, by way of ex- 

 ample, fruit-sugar or levulose, grape-sugar or glucose, 

 glycogen, manna, milk-sugar, etc.; these substances 

 exert no attraction upon the movements of the sper- 

 matozoids, whereas cane-sugar exercises an attraction 

 so powerful that the capillary tube becomes at once 

 crammed with them. The excitation first induces in 

 the spermatozoid a movement of direction: the body 

 is brought into a position enabling it to reach the tube 

 by movement in a straight line. The same phenome- 

 non has been observed by Strasburger in the case of 

 Algae zoospores; when these minute beings are at- 

 tracted by a chemical or luminous excitation, the first 

 thing that happens is the directing of the body 

 towards the attracting source. 



A solution of one in one thousand parts is suffi- 

 ciently concentrated to draw the spermatozoids of 

 Mosses into the capillary tubes. The " threshold of 

 excitation" for them, accordingly, is the same as for 

 the spermatozoids of ferns. Furthermore, Weber's 

 law is in this instance again verified; only, in order to 

 have the chemical excitation produce a different at- 

 traction, it must be stronger than the first in the pro- 

 portion of 50 to 100. In the experiments upon the 

 spermatozoids of ferns the ratio is a little smaller; be- 

 ing only 30 to 100. 



The question presented itself to the author as to 



