THE ZYGNEMACEiE. 
320 
modern conception that without a gamogenetic act the 
permanence, within certain limits, of a species cannot he 
maintained ; and that mere vegetative growth or increase 
must ultimately result in its extinction. Indeed the modern 
belief that gamogenesis takes place at some period in the 
life-history of all species of plants, however humble, is 
constantly receiving the sanction of experience. 
The student of the Fresh-water Algie will be a continual 
witness to their recuperative power. He will constantly see 
how nature foiled in one process instantly initiates another in 
the endeavour to restore the balance. Let him betake himself 
to the nearest pond or ditch and make a gathering of vigorously 
growing Vaucheria ; then slightly rupturing a cell-wall, let him 
place the plant in water under his microscope and watch what 
ensues. He will see portions of the protoplasmic contents of 
the ruptured cell flowing out in an apparently oily stream, but 
as soon as they come in contact with the watery medium 
breaking up and contracting into spherical and other masses 
which immediately throw around themselves a protective 
skin, or envelope; in other words, he has witnessed the 
formation of gonidia-like bodies presumably possessing the 
power to germinate, and ultimately to grow into plants like 
that from which they emanated. The portions of the proto¬ 
plasm left in the cell also contract into globular masses 
which acquire apparently a cellulose coat. Hanstein has 
also observed that if a filament of Vaucheria becomes injured, 
the protoplasm of the injured part immediately contracts and 
protects itself by a septum which shuts it off from the injured 
part. 
Certain somewhat analogous proceedings frequently take 
place in those cells of the Zi/f/nemacece which fail to perform 
their function ; the loss of the normal act being apparently 
partially compensated by the formation of other bodies, 
presumably capable of reproducing the likeness of the parent 
plant, out of the coutents of the cells. 
Reproduction in the Fresli-water Algie by means of 
zoogonidia is nature’s mode of providing for the dissemination 
of a species. This form of increase does not, it seems, 
normally occur in the Zytjnemacea; but, as I have just 
observed, in cells not conjugating, or otherwise failing to 
perform their function, certain apparently abnormal pro¬ 
ceedings take place. These are the differentiation of the 
plasma of the cell into certain rounded bodies which become 
encysted, thus simulating a resting form of zoospore ; or 
numbers of nearly colourless zoogonidia are formed out of 
the cell contents. On one occasion I witnessed the emission 
