XIV. ALG^E. 977 



protuberance at its extremity, bursts there, and the zoospores escape, the first with impetuosity, the 

 others more slowly ; they are turbinate in shape, and furnished with two hairs. This is not the only 

 mode of reproduction possessed by Saprolegnia ; another phenomenon succeeds. The filaments emit small 

 lateral branches, the extremities of which swell into sacs of a blackish hue, due to the condensation of their 

 granular contents. Soon a septum forms, isolating the sacs from the little tubes which serve as pedicels 

 to them. After some time the granular matter divides into several masses, which at first adhere to the 

 walls of the sac, but which later become free and spherical. Sometimes there is only one of these 

 masses ; sometimes the same sac contains fifteen or twenty. I have fancied that I could recognize 

 on their periphery little mamillce resembling regularly arranged opercula.' The sacs have been termed 

 by Pringsheim oosporanyia. The oosporangia require fertilization to enable them to produce fertile 

 spores. It is obvious, therefore, that Saproleyniea have a double mode of reproduction, similar to that of 

 Vaucheria: the one asexual by means of zoospores ; the other sexual, producing ouyonia arista"- from the 

 fertilization of a sporangium (posporangiwri). 



In retaining Saprolegntea amongst Algee, we are necessarily led to connect with them some plants 

 which appear to approach them in their mode of reproduction by zoospores, but which some distinguished 

 botanists also place amongst Fungi ; these are Cystopus, Peronospora, &c. ; as well as the small family of 

 (Jhytridiacea, comprising Rhizidium, Chytridium, Synchytrium, &c. The great differences of opinion as to 

 the nature of these plants which exist, show how obscure is the whole history of those Cryptogams that 

 possess no archegonia. 



TRIBE V. SYNSPORE^, Decaisne. CONJUGATE, Link. 



Fresh-water Algce, consisting of cells of very various form, or of chambered tubes 

 containing green matter, either granular or disposed in spiral plates. At the period 

 of reproduction, the cells forming each tube swell or inamillate laterally, and the 

 nmmillae of two contiguous tubes then unite, and their walls disappear at the surface 

 of contact. Communication being thus established between the two cells, the green 

 matter of the one passes into the cavity of the other, and mixes with its contents, 

 and from this fusion simple or compound spores result, which produce one or several 



new plants. 



PRINCIPAL GENEEA. 



Zygnema. Mougeotia. Craterospermuin. Spirogyra. 



Zygouium. Staurospermum. Sirogonium. Mesocarpus. 



SUB-TRIBE. DESMIDIE^E. 



Microscopic green Algce, presenting the appearance of corpuscules composed of 

 two opposite hemispheres, joined base to base, free, isolated, or associated in flat or 

 spiral bands, enveloped in mucilage, very varied and elegant in form, always symme- 

 trical, entire or lobed, surface smooth or sculptured, reproduced either by conju- 

 gation (as in Synsporece) and the passage of the endochrome from one half to the 

 other, resulting in a reproductive spore, or by the division of an individual, or 

 by means of sporangia of very various forms. The green matter of Desmidiece pos- 

 sesses, according to M. de Brebisson, a circulation analogous to that of Chara. 



PRINCIPAL GENERA. 



3 E 



