C YSTOSPERME^. 183 



of tliG plant wlilcli occur towards the completion of the pro- 

 cess of reproduction, drawing along with them, and thus rup- 

 turing, the slightly clastic membrane of the cells. (PI. xvii. 



%• 7.) _ 



" AYithout some such beautiful and effectual provision, it 



will be evident, on reflection, that the spores would have to 

 remain immured within their narrow cells for an indefinite 

 length of time, even until, perhaps, their vitality had ceased 

 and the cells had become their coffins ; for occupying, as the 

 spores do, but a portion of the space of the cells, and enve- 

 loped as they are in membranes, they can themselves, of 

 course, exert no influence in producing the rupture of the 

 walls of those cells. 



" In all the ConfervcB with which I am acquainted, some 

 special means are provided for the escape of the spores or 

 zoospores, their liberation never being left to the sole agency 

 of decomposition of the tissue of these plants ; thus, in the 

 majority of the branched Confervce, and in the species of the 

 genus SphcBrojjlea as well as in many other Confervce, their 

 liberation is effected by the rupture of the cells in which 

 they are contained, which rupture is occasioned by the deve- 

 lopement of the zoospores while still inclosed within the cells ; 

 in Conferva (^Microspord) glomerata a special aperture exists 

 for the escape of the zoospores at the period of reproduction, 

 situated at one side of the distal extremity of each cell ; in 

 the Conjugating tribe the zoospores pass out through the 

 openings of the connecting tubes of the cells, which, when 

 reproduction has been completed, separate from each other; 

 and lastly, in the Vesiculiferce, as has been shown, a more 

 complicated provision exists for the egress of the spores and 

 zoospores. 



" Of all characters whereby the VesiculifercB may be distin- 

 guished from other ConfervoB, that derived from the corruga- 

 tion of the investing sheath is perhaps the most valuable, 

 from the circumstance not merely of its being confined to the 

 species of that genus, but from its constant presence in all 

 stages of their developement ; and not only is it interesting as 

 being indicative of a Vesiculifera, but also as pointing out 



N 4 



