CHAP, i.] Theory of Evolution and Epigenesis. 405 



a hybrid between a goat and a cow, and other similar ones, 

 and he is angry with Koelreuter for fixing such narrow limits 

 to the occurrence of hybrids ; thus the first person who 

 produced hybrids systematically in the vegetable kingdom 

 must submit to be scolded for refusing to accept the imaginary 

 hybrids of his contemporaries. Gleichen's book and t he- 

 selection from his microscopic discoveries, which appeared in 

 1777, abound in good detached observations ; he was the first 

 who saw and figured the pollen-tubes of Asclepias, without of 

 course suspecting their real nature and importance. 



Kaspar Friedrich Wolff is usually said to be the writer who 

 refuted the theory of evolution. It is certainly true that in 

 his dissertation for his doctor's degree in 1759, the well-known 

 ' Theoria generationis,' he appeared as the decided opponent 

 of evolution ; but the weight of his arguments was not great, 

 and the hybridisation in plants which was discovered at 

 about the same time by Koelreuter supplied much more 

 convincing proof against every form of evolution. Wolff 

 conceived of the act of fertilisation as simply another form of 

 nutrition. Relying on the observation, which is only partly 

 true, that starved plants are the first to bloom, he regarded the 

 formation of flowers generally as the expression of feeble 

 nutrition (vegetatio languescens). On the other hand the 

 formation of fruit in the flower was due to the fact, that the 

 pistil found more perfect nourishment in the pollen. In this 

 Wolff was going back to an idea which had received some 

 support from Aristotle, and is the most barren that can be 

 imagined, for it appears to be utterly incapable of giving any 

 explanation of the phenomena connected with sexuality, and 

 especially of accounting for the results of hybridisation. Wolff 

 may have rejected the theory of evolution on such grounds as 

 these, but he failed to perceive what it is which is essential 

 and peculiar in the sexual act. 



