Specificity in Fertilization 93 



When the liquid in the tube contains only o.oi per cent, 

 malic acid the spermatozoa of ferns very soon move toward 

 the opening of the capillary tube and within from five to 

 ten minutes many hundreds of spermatozoa may accumu- 

 late in the tube. The malic acid acts as well in the form 

 of a free acid as in the form of salts. 1 



These experiments were continued and amplified by 

 Shibata. Bruchmann 2 found that the spermatozoa 

 of Lycopodium are positively chemotactic to citric acid 

 and salts of this acid, although no citric acid could be 

 shown in the contents of the archegonia. They are 

 also positively chemotactic to the watery extract from 

 archegonia. 



Dewitz, Buller, and the writer have vainly tried to 

 prove the existence of a positive chemotropism of 

 spermatozoa to eggs of the same species. Lillie claims 

 to have proved a positive chemotropism of the sperm 

 of sea urchins to "fertilizin, " but such a conclusion is 

 only justified if a method similar to that of Pfeffer's 

 with capillary tubes, gives positive results; such a 

 method was not used in Lillie's experiments. It seems 

 that the fertilization of the egg by sperm is rendered 

 possible by two facts ; first that where fertilization takes 

 place outside the body egg and sperm are shed simul- 

 taneously by the two sexes. This can be easily ob- 



1 Pfeffer, Untersuchungen aus dem botanischen Institut zu Tubingen, 

 1881-1885, i., 363. 



2 Bruchmann, H., Flora, 1909, ic., 193. 



