THE ALG 225 
288. Discussion. — Gdogonium is a plant of decidedly 
higher type than Spirogyra. While the nutrition of both 
plants is much alike, Gdogonium shows a decided advance 
over Spirogyra in the structure of the vegetative filaments, 
inasmuch as these are not alike at both ends, but have a 
definite cell which serves as a holdfast and.a terminal cell 
different from the others of the filament. 
The sexual reproduction of Gdogonium is accomplished 
by the union of unlike gametes (sperm and egg-cell) and 
is therefore higher in type than that of Spirogyra in which 
the gametes appear to be alike. The small size of the 
sperms enables them to accomplish the fertilization of 
the egg with the expenditure of only a trifling amount 
of material, and the motility of the sperms enables them to 
reach the egg quickly, instead of drifting against it as one 
filament of Spirogyra drifts against another. Economy and 
certainty in the process of sexual reproduction are features 
of the progress of plants from lower to higher forms. 
In some species of Gdogoniwm the antheridia are pro- 
duced on small short filaments called dwarf males. These 
are developed from zodspores which attach themselves to 
the female filament or to the odgonium. 
VAUCHERIA, ONE OF THE GREEN ALGH 
289. Occurrence. — Vawcheria, or green felt, is one of 
the rather widely distributed green algz, some species 
being found in salt water and others in stagnant fresh 
water, sometimes in fresh running water or on damp soil. 
V. sessilis, the commonest species, occurs covering the 
earth of pots in greenhouses. When growing on earth it 
is rather easily recognized by its dark green color and the 
