INTRODUCTION TO CRYPTOGAMIC BOTANY. 119 



selves, too, are for the most part oblong, and point already to 

 some of the lower Desmidiacew. In Palmoglcea Mene- 

 ghinii, at least, there is a distinct coupHng of neighbouring 

 spores ; and Brebisson has noticed a similar fact in Coccochloris 

 protuberans and rubescens, while the transparent peduncles 

 point in the direction of certain Diatomacece. The limits of 

 this group are uncertain, from the true nature of all the spe- 

 cies being at present imperfectly known, and, consequently, 

 some of the more compact forms, such as Entophysalis, Hy- 

 drococcus, and Palmophyllum, may, for the present, oscillate 

 between this group and the last. In such plants as Palmella 

 botryoides, Mr. Thwaites does not consider the bodies figured 

 at the tips of the threads as spores, but as more properly buds, 

 since true fruit is formed in some, by conjugation, and in 

 others, by the conversion of the endochrome into zoospores. 

 The suggestion is one of considerable value, and has an im- 

 portant bearing on those Algae, which, like Glwocapsa and 

 Nostoc, seem multiplied solely by division of the endochrome. 

 It should be observed that these bodies, after a time, put on a 

 form precisely like that represented in OloeocaiJsa Hookeri 

 (Fig. 28). The curious genus, Entospeira, leads through S'pi- 

 rotcenia to Zygnenna. Palmodyctyon, Kiitzing, which is pre- 

 cisely the same thing with Trypothallus, Hook, and Harv., is 

 evidently a member of the Protococcoid group. According as 

 the endochrome divides, vertically or transversely, the mass 

 increases in width or length ; and as this division alternates 

 after some tolerably fixed law, a network of greater or less 

 width is formed, according to the proportion of vertical to 

 horizontal division. 



2. Desmidiace^. Ralfs. 



Cells void of silex, free, or forming brittle threads or minute 

 fronds, increased by the formation of two new half cells in the 

 centre, so that the two new cells consist each of a new and old 

 half cell. Spores generated by the conjugation of two distinct 

 individuals. 



97. The genus Entospeira leads directly to Spirotcenia, 

 a member of one of the most beautiful, varied, and singular 

 group of Alg£e, which has been admirably illustrated by Mr. 



