Mr. J. Ralfs on the Nostochinez. 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. 
8rd. 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 Conjugate and Desmidice. When they are fully 
developed the filament has fulfilled its function, separates into 
single joints and disappears. The sporangia m Nostoe and Tri- 
chormus differ but little except in size from the ordinary joints, and 
are more or less orbicular. In Spherozyga and Cylindrospermum 
they are either elliptic, oblong or cylindrical. 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 I cannot doubt ; 
but the nature of the vesicular cells is less certam. 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 Oscillatoriee, 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 Nostochinee 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 
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