Each segment however has a central inflation, which causes the end view to be more or less cruciform. The plants belonging to the second section are also compressed, and, like those in the preceding, their front view differs from the lateral one and has a linear notch on each side. In the first section the segments are compressed, and in the front view, which differs from the lateral one, they are united by a portion only of their bases, and thus the constriction forms a linear notch on each side. The species belonging to Cosmarium may conveniently be divided into three sections. ![]() Tetmemorus differs from this genus in its elongated fronds and emarginate extremities. In Cosmarium the fronds are never elongated, are always constricted in the middle, and the starch vesicles are scattered. Those having cylindrical fronds in some respects show an affinity with Penium but in that genus the constriction is either wanting or obscure, and the segments are longer than broad. Under Micrasterias, Euastrum, and Xanthidium, I have given my reasons for differing from such highĪuthorities, and pointed out the characters which distinguish those genera from Cosmarium.īoth Ehrenberg and Meneghini consider the inflato-compressed segments essential but some species with globular or cylindrical segments can by no means be separated from the compressed ones. ![]() Meneghini for the most part followed this arrangement, merely changing the name to Cosmarium, which had a prior claim, and also adding some species taken from Xanthidium. The fronds are minute, simple, constricted in the middle the segments are generally broader than long and inflato-compressed, but in some species orbicular or cylindrical they are neither emarginate at the end nor lobed at the sides, and have no spines or processes.Įhrenberg united plants belonging to this genus with others having lobed segments, in order to form his genus Euastrum. RALFS: The British Desmidieae - Cosmariumįrond simple, constricted in the middle segments as broad as or broader than long, neither sinuated nor notched.
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