CYSTOSPERMEiE.

183

of the plant which occur towards the completion of the pro-cess of reproduction, drawing along with them, and thus rup-turing, the slightly elastic membrane of the cells. (PL xvii.%• 7 -)

“ Without some such beautiful and effectual provision, itwill be evident, on reflection, that the spores would have toremain immured within their narrow cells for an indefinitelength of time, even until, perhaps, their vitality had ceasedand the cells had become their coffins; for occupying, as thespores do, but a portion of the space of the cells, and enve-loped as they are in membranes, they can themselves, ofcourse, exert no influence in producing the rupture of thewalls of those cells.

“ In all the Conferva with which I am acquainted, somespecial means are provided for the escape of the spores orzoospores, their liberation never being left to the sole agencyof decomposition of the tissue of these plants; thus, in themajority of the branched Conferva, and in the species of thegenus Spharoplea as well as in many other Conferva, theirliberation is effected by the rupture of the cells in whichthey are contained, which rupture is occasioned by the deve-lopement of the zoospores while still inclosed within the cells;in Conferva (Microspora) glomerata a special aperture existsfor the escape of the zoospores at the period of reproduction,situated at one side of the distal extremity of each cell; inthe Conjugating tribe the zoospores pass out through theopenings of the connecting tubes of the cells, which, whenreproduction has been completed, separate from each other;and lastly, in the Vesiculifera, as has been shown, a morecomplicated provision exists for the egress of the spores andzoospores.

“ Of all characters whereby the Vesiculifera may be distin-guished from other Conferva, 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 thespecies of that genus, but from its constant presence in allstages of their developement; and not only is it interesting asbeing indicative of a Vesiculifera, but also as pointing out