CHAP.V.] the Influence of the Knowledge of Cryptogams. 207 



the escape of the zoospores of Vaucheria. The remarkable 

 thing is, not that such views were entertained, but that the 

 majority of botanists combined with them a belief in the 

 constancy of species. But this dogma rendered good service 

 to the science in this instance, for the botanists, who at a later 

 time applied themselves to the systematic examination of the 

 Algae and Fungi, confided in the constancy of the processes of 

 development in each species, which they expected would assert 

 itself in these forms as in the Mosses and higher plants. 



With much that was obscure and doubtful, the result of 

 occasional observation accompanied by uncritical interpreta- 

 tion, the literature of the subject had contained for some time 

 a certain number of single well-established facts of real import- 

 ance, which were well adapted to serve as starting-points for 

 earnest and exact investigation. Among the Algae the genera 

 Spirogyra and Vaucheria especially had supplied remark- 

 able phenomena ; Joseph Gartner observed the formation 

 of zygospores in Spirogyra in 1788, Hedwig saw in the mode 

 of their production at least a suggestion of sexuality (1798), and 

 Vaucher 1 , in his * Histoire de Conferves d'eau douce,' which 

 appeared in 1803 and was far in advance of its time, called 

 conjugation distinctly a sexual process ; the optical means at 

 his disposal did not enable him to observe the fertilisation in 

 Vaucheria (Ectosperma), which was named after him, though 

 he described the sexual organs accurately ; the movement also 

 of the zoospores in this genus escaped him, and Trentepohl 

 first observed their escape and swarming in i8o7 2 . Vaucher 

 had also observed the formation of new nets in the old cells 

 of Hydrodictyon, and Areschoug repeated the observation in 

 1842, when he saw the swarming of young cells in the old 

 ones. Bischoff, as early as 1828, saw the spermatozoids of 



1 Jean Pierre ^tienne Vaucher, the instructor and friend of P. de Candolle, 

 was a minister and professor in Geneva. 



2 Trentepohl's communication is to be found in the ' Botanische Bermer- 

 kungen und Berichtigungen ' of A. W. Roth, Leipsic, 1807. 



