IOWA ACADEMY OF SCIENCES. 31 



decisive experiments on close and cross fertilization by Gled- 

 itsch about the middle of the century, and the thorough and 

 wide reaching experiments of Koelreuter, from 1761-1766, who 

 produced hybrids by cross fertilization, the question of the 

 sexuality of plants continued a matter of dispute until finally 

 settled by Gilrtner, who collected the evidence from the work 

 of his predecessors, added it to his own resulls of experiments 

 extending over twenty-five years and combined all in a volume 

 published in 1849. 



The study of the fact of sexuality necessarily involved the 

 study of the functions of the pollen and ovule in fertilization, 

 and here again there was much controversy among those who 

 accepted sexuality, which ended so far as flowering plants are 

 concerned wi'h the discovery of the descent of the pollen tube 

 and its influence upon the egg-cell, by Amici in 1846. Tne 

 reproduction of the cryptogams was generally thought to be 

 a sexual. 



In 1657 Harvey, the discoverer of the circulation of the blood, 

 declared that all living things come from an ovum by differen- 

 tiation, and that the ovum might proceed from patents or arise 

 spontaneously. Twenty years later, Hamen discovered the 

 spermatazoa, which he regarded as the young, which required 

 only to be nourished by the ovum. Here we have two theories 

 of reproduction that were at war for more than a century and 

 a half. 



Wolff, who first studied the development of the chick under 

 the microscope, described the blastoderm in 1759, and its dif- 

 ferentiation into organs, contrary to the general opinion held 

 by Grew, Buffon and Haller that the embryo was a complete 

 being like the bud of a tree, whose growth was merely an 

 unfolding. It was in 1827 that Von Baer discovered the ovum 

 of mammals, traced its development and laid the foundation of 

 Embryology. 



The seventeenth century saw good beginnings ia histology 

 and Comparative Anatomy of animals. Malphigi studied the 

 anatomy of insects; Leuwenhoek discovered striated muscle- 

 fiber and epidermal cells. Swammerdam studied the anatomy 

 of insects, molluscs and the metamorphosis of insects. It may 

 be said, however, that in the eighteenth century such studies 

 were largely superseded as in Botany by classification, and were 

 not again seriously taken up until the rise of Comparative 

 Anatomy with Lamarck, St. Hilaire, Meckel and Cuvier. 



