224 ELEMENTS 
OF BOTANY. 
conjugation by leaving the Spirogyra filaments in very cold water over 
night, and in this way the successive steps of the conjugating process 
may be studied by daylight. 
In such ways the series of phenomena 
shown in Fig. 195 has been clearly made out. If the student cannot 
Fic. 195. — Formation of Spores 
by Conjugation in Spirogyra. 
A, two filaments of Spirogyra side by 
side, with the contents of adjacent 
cells uniting to form spores z At 
the bottom of the figure the pro- 
cess is shown as beginning, at the 
top as completed, and the cells of 
one filament emptied; B, a single 
filament of another kind of Spiro- 
gyra, containing two spores, one 
lettered z. (A magnified 240 diame- 
ters, B 150 diameters.) 
follow these operations under the mi- 
croscope, he may at least by looking 
over the yellower portions of a mass of 
Spirogyra find threads containing fully 
formed zygospores, like those shown 
in B, Fig. 195. 
ALG. 
274. Characteristics of Alge. 
— The Protococcus and the Spi- 
rogyra are two common fresh- 
water examples of the kind of 
plants classed under the general 
name of Alge, a group of which 
the largest and most interesting 
examples are to be found among 
the seaweeds. Alge are all 
aquatic, or at least live usually 
in damp places; they contain 
chlorophyll, and are therefore 
capable of absorbing carbonic 
acid gas and fixing carbon; few 
algee are parasitic or saprophytic. 
In fact, the main distinction be- 
tween this group and the fungi 
hes in the self-supporting char- 
acter of the former plants and 
the parasitic or saprophytic 
(§$ 151) character of the latter. For this reason the two 
groups, based on the characteristic behavior or mode of life of 
their members, rather than on the real relationships of the 
