CHAP, v.] the Influence of the Knowledge of Cryptogams. 209 



in making its sexual propagation, the first commencement 

 of the embryo, the starting-point of the investigation. It 

 was natural to expect as happy results from the embryology 

 of the Algae, as had been obtained in the case of the 

 higher plants; it was important therefore, that the observer 

 should no longer rest satisfied with a knowledge of the sexual 

 multiplication of the Algae ; he must enquire into their asexual 

 propagation, and by its aid discover the complete history of 

 their development. Former observations suggested the pro- 

 bability that here too sexual propagation is the prevailing 

 rule ; but it was easy to foresee that it would be a task of 

 great labour to make out a connected history of develop- 

 ment, a task of which the collectors who liked to call them- 

 selves systematists had never formed a conception ; but 

 Nageli's and Hofmeister's researches had made botanists 

 familiar with the highest demands of this kind, and the men 

 who were to gain new conquests for genuine science were 

 already engaged in the work in 1850. A splendid result 

 appeared in 1853, in Thuret's account of the fertilisation of 

 the genus Fucus ; this was a simple process as a matter of 

 embryology ; but the sexual act was so clear, and even open 

 to experimental treatment, that it threw light at once upon 

 other cases more difficult to observe. Then followed dis- 

 coveries of sexual processes in rapid succession; Pringsheim 

 solved the old enigma in Vaucheria in 1855, and between 

 1856 and 1858 in the Oedogonieae, Saprolegnieae and 

 Coleochaetae ; in 1855 Cohn observed the sexual formation 

 of spores in Sphaeroplea. Pringsheim however was not 

 content with carefully observing the sexual act; he gave 

 detailed descriptions of growth in the same families in its pro- 

 gress cell by cell, of the formation of the sexual organs, and the 

 development of the sexual product. The asexual propagations 

 which are intercalated into the vegetation and embryology were 

 shown in their true connection. Processes were recognised 

 which often recalled the alternation of generations in the Mus- 



p 



