Mr. J. Ralfs on the Nostochinese. 323 



cells by a minute orifice at each end, which in situ looks like a 

 minute globule; by this peculiar appearance and by the ab- 

 sence of granular matter the vesicular cells may be easily recog- 

 nized. 



3rd. Enlarged cells or sporangia. — These are produced by en- 

 largement of the ordinary cells, and are the last formed. They 

 are filled with a dense granular matter which becomes homoge- 

 neous and opake, and finally turns from green to brown like the 

 sporangia in the Conjugatce and Desmidiece. When they are fully 

 developed the filament has fulfilled its function, separates into 

 single joints and disappears. The sporangia in Nostoc and Tri- 

 chormus differ but little except in size from tlie ordinary joints, and 

 are more or less orbicular. In ^phcerozyga and Cylindrospennum 

 they are either elliptic, oblong or cyhndrical. Usually they are, 

 even before the appearance of granular matter, easily distin- 

 guished from the vesicular cells by the absence of the remarkable 

 puncta-like globules I have just noticed. The sporangia continue 

 to enlarge after their separation from the filament. 



That these enlarged cells are true sporangia 1 cannot doubt ; 

 but the nature of the vesicular cells is less certain. The coex- 

 istence of the vesicular cells and sporangia in the same filament 

 may lead to a better understanding of their office in other tribes. 

 As the former are evidently of the same nature as those present 

 in Rivularia and in some of the Oscillatorica, we cannot pro- 

 nounce that they are reproductive organs in the one family and 

 not in the other. 



On the present occasion I shall examine only those genera of 

 the Nostochinece in which the plant forms a stratum. As I have 

 before remarked, they form more or less extended patches, either 

 on the damp soil or on aquatic plants, or at the bottom of pools 

 and ditches. Their colour is bluish green or verdigris, and the 

 stratum is extended by the filaments radiating at its margin. 

 Hence both in colour and habit, as well as in general appearance, 

 they resemble species of Oscillatoria ; the stratum, however, is 

 usually more tender and gelatinous. The mass, which in an 

 early state is somewhat translucent, at length commonly becomes 

 opake and presents a pulverulent appearance. 



The facility with which the filaments break up, especially in 

 warm weather, considerably increases the difficulty of studying 

 these plants. When the plant is mature, the destruction of the 

 filament so frequently takes place in a few hours, even though it 

 be kept in water, that recent specimens forwarded to any distance 

 seldom arrive in a condition fit for examination ; I am therefore 

 less able to profit by the examination of those sent me from other 

 districts. Even when they are mounted in fluid, the labour is 



21* 



