and to guide themselves, the former to their relative gymnospores, the latter to appropriate places whereon to rest and recommence the process of germination and growth.
In the methods of fructification, moreover, the resemblances between flowering plants and Algæ are probably as close as in any other particular. Setting aside the Volvocineæ, Palmellaceæ, and some others in which the process of multiplication is merely a process of cell division, either intrinsic or extrinsic, we find in the Confervæ, Siphonaceæ, Oscillatorieæ, etc., that the single cell has the power of producing reproductive spores, thus (keeping in mind that an algal cell is the equivalent of a phænogamic flower) affording an analogy with the class of so-called hermaphrodite flowers. A strictly monœcious form of fertilization is met with in the Œdogoniaceæ, where the contents of certain inflated cells are vivified by the contents of contiguous antheridial cells which, by rupture of the cell division, gain access to the inflated cells. A distinct advance upon this method is found in many Œdogonia and Chætophoræ. Here the distinction between antheridial and sporidial cells is evident—they often occur upon different filaments, though sometimes upon distant portions of the same, and are easily recognized by their shape and appearance. The contents of the antheridial cell (androspore) when mature escape through rupture of the cell wall, and, being furnished with cilia, lead an active locomotor life until, coming in contact with the gonidial cell (oospore), the locomotion comes to an end and the contents of the two combined form a zoospore which eventually becomes a young plant.
The Zygnemaceæ are veritable diœcious plants, and propagate by a process of conjugation—the cells of two contiguous filaments throw out a connecting tube through which the contents of one (the antheridial) cell pass into the other (the gonidial), and thus fertilize them, the result being a zoospore. In this process the fertilization of the ovule by the pollen tube in Phanerogams is closely imitated. But further, that abnormal self-fertilization that takes place in certain flowers under unusual conditions, and which is termed cleistogamy, would appear to occur at times in certain Spirogyræ, the filaments of which have the power of producing zoospores—the so-called pseudogonia—in certain cells without conjugation; in fact these cells are, like the cleistogamous flowers, not only hermaphrodite, but contain within themselves the power of self-fecundation.
In the following list of fresh-water Algæ which have come under my observation during the last eighteen months I have included only such as I feel pretty certain I have verified. Many others are not enumerated, because I am at present doubtful of their classification; but with further search and observation I have no doubt the list may be extended indefinitely.
