Chap. IV.] f rom ^38 to I 85 1. 



the wall without the cell. Since the contents are the essen- 

 tial part of the cell and form a separate and individual whole 

 which has its own membrane-like boundary, the primordial 

 utricle, before the secretion of the membrane of cellulose, we 

 must either confine the term cell to the enveloping mem- 

 brane or to the chamber which it forms and find another 

 name for the body of the contents, or else call this the true 

 and proper cell. This, which presents itself at once as the 

 correct mode of conception to anyone who observes the 

 formation of swarm-spores in Algae and Fungi and many 

 other cases of cell-formation, was from this time forward a 

 vital point in the doctrine of the cell. Braun contributed 

 also to the clearing up of the ideas of botanists on this sub- 

 ject by bringing together under one systematic view and 

 classifying all the varieties of cell-formation which were known 

 to him up to the year 1850, and especially by a more 

 searching investigation into modes of conjugation. Henfrey's 

 contributions ('Flora' of 1846 and 1847) rested entirely 

 on the observations of German botanists, and brought to 

 light nothing that was independently and essentially new. 

 On the other hand Hofmeister's new observations on the 

 development of pollen (1848), and his many remarks on 

 cell-formation in his epoch-making researches into embryo- 

 logy in 185 1, contributed repeatedly to the deciding of doubtful 

 points, especially in the behaviour of the nucleus in cell-forma- 

 tion and the production of the dividing walls. Von Mohl, 

 who in spite of his own excellent observations maintained up 

 to 1846 a somewhat undecided attitude of mind in respect 

 to Schleiden's theory, which was at that time still in vogue, 

 published in 185 1, in his treatise 'Die vegetabilische Zelle,' 

 an excellent summary of the results which had been so 

 far achieved. In describing cell-division he notices speci- 

 ally that the new nuclei occupy the centres of the future 

 daughter-cells before the division of the contents commences ; 

 but he still clung to his old view, that in every instance of 



