CHAP.V.] the Influence of the Knowledge of Cryptogams. 199 



as in animals was effected by spermatozoids. A perfect insight 

 into the embryological conditions in question could only be 

 obtained when the embryology of the Phanerogams especially 

 had been cleared up, for according to Schleiden's theory, which 

 made the pollen-tube enter the embryo-sac in the ovule and 

 develop into the embryo, the ovule was no longer to be 

 regarded as a female sexual organ, but only as a place of incu- 

 bation for the embryo, which was thus really produced asexually. 

 This important question was set at rest by WILHELM HOFMEIS- 

 TER'S work, ' Die Entstehung des Embryos der Phanerogamen,' 

 which appeared in 1849. In this work, and in a series of sub- 

 sequent treatises, he showed that the egg-cell is formed 

 in the embryo-sac before fertilisation, and that it is this which 

 is excited to further development by the appearance of the 

 pollen-tube, and produces the embryo. Hofmeister had 

 observed the organisation of the ovule, the nature of the 

 embryo-sac, and of the pollen-grain, and the formation of the 

 embryo from the fertilised egg-cell step by step and cell by cell, 

 and his account of these processes was aided by the light which 

 Nageli's theory of the cell, and his reference of all processes of 

 development to the processes of cell-formation, had thrown 

 upon the history of development. He went on to apply the 

 same method to the study of the embryology of the Muscineae 

 and the Vascular Cryptogams, and followed the development 

 of the sexual organs cell by cell in a large number of species ; he 

 observed the origination of the egg-cell which was to be subse- 

 quently fertilised, and the formation of spermatozoids, and above 

 all he showed the divisions which take place in the fertilised 

 egg-cell, and the relation of its segments to the further growth of 

 the sexual product in course of formation. The whole course 

 of development in the Muscineae and Vascular Cryptogams 

 displayed a return twice repeated to the single cell as the 

 starting-point in each case of a new phase of development ; the 

 true relation between the asexually produced spore and its 

 germ-product on the one side, and the sexually generated 



