74: THE AMERICAN MONTHLY [April, 



earth, remember, nothing ranking below them but the Lichens and 

 Fungi. 



But the sea-weeds bear an unfortunate name, for many of them are 

 fresh-water plants. Let us say algce therefore, which, though meaning 

 the same, does not strike the English ear so unpleasantly ; and then we 

 have salt-water algae and fresh-water algae, and among the latter we 

 come, upon the desmids. Remembering then that no desmids are ever 

 found in salt-water, we can ignore that whole division and confine our- 

 selves to the fresh-water plants. 



The fresh-water algae include some twenty families, viz : i, Leman- 

 eacece ; 2, Porphyracece ; 3, Batrachospermacece ; 4, Hildibrandtia- 

 cece ; 5, Coleochcetacece ; 6, CRdogoniacece ; 7, Sphceropleacece ; 8, 

 Cortfervacece ; 9, Pithophoracece ; 10, Vaucheriacece ; 1 1 , Botrydia- 

 cece ; i2,Volvocacece ; 13, Protococcacece ; 14, Palmellacece ; i$,Chy- 

 tridicce ; 16, Conjugatce ; 17, Desmidiece ; 18, Diatomacece ; 19, JVos- 

 tockacece ; 20, Chroococcacece. That is to say, the desmids and the 

 diatoms are in the same general group with all the rest of these families. 

 These fall again into two divisions ; the filamentous and the cellas form 

 algae, and there happen to be the same characteristics in the family of 

 desmids. This may cause the student some trouble. He may mistake 

 some other filamentous or cell-shaped species of algae for a desmid.. 

 What is the distinction ? This : that the filamentous desmids are notched 

 in the middle of each cell, giving a wavy or toothed appearance to the 

 outline ; the other filamentous unbranched algae never so. There is but 

 one exception. Gonatozygon might be taken for one of the brown Os- 

 cillariece, of the family Nostochacece. But the cells in Oscillaria and 

 allies are never much longer than wide, while in Gonatozygoit they are 

 10-20 times longer than wide. Of the cell-shaped forms, again, two 

 other families will bother him, the Palmellacece and the Diatomacece , 

 which are also free one-celled algae. But the symmetry or bilaterality 

 of the cell will distinguish the desmids from the former, and their mo- 

 tion and color in addition from the latter. The desmids are remarka- 

 ble for their symmetry. The human form is symmetrical, but the desmid 

 still more so. Given the outline of half the man, on a line drawn from 

 head to foot, and one can draw the man entire ; but we need only to 

 see a quarter of the desmid to complete the figure in almost every case, 

 Closterium being the single exception. The quarter reversed gives the 

 half, and the half reversed gives the whole figure. As illustrations take 

 Micrasterias, Cosmarium, Dociditim, Xanthidium, StaurastruiTi. 

 The only exceptions are Closterium (whose shape makes it known at 

 once), and some others in the early stages of multiplication, as, for 

 example, Micrasterias. Now it is true that in the Palmellacece each 

 quarter is like every other quarter, but there is no bilaterality, no fissure 

 which divides the cell into two halves, each the exact counterpart of 

 the other. And this distinction will separate the diatoms also, for though ' 

 there is here symmetry — bilaterality — it is differently produced. In the 

 diatoms it is effected by a band or hoop which runs across the long di- 

 ameter ; in the desmids by a division across the short diameter. The 

 bilaterality of the diatom may be represented by a pill-box standing on 

 edge with a narrow strip pasted on the middle of the circumference ; 

 that of the desmid by a tube with a groove running round the middle 

 between the two ends. But we seldom get this view of the diatom any 



