SOME TYPES OF FLOWERLESS PLANTS. 225 
latter, are not certain hereafter to be recognized in any strictly 
scientific classification of cryptogamous plants. 
Algze vary in size from spheres ,5-455 imch in diameter 
to great cable-like masses many hundreds of feet in length. 
Some species are found in salt, some in brackish, some in 
fresh water. There are species which occur growing on snow 
and melting ice, while others form the characteristic vegeta- 
tion of hot springs, in which they sometimes endure a tem- 
perature nearly equal to that of boiling water. 
275. Reproduction in Alge. 
— The reproductive processes 
in alge are of several types, 
which are described in special 
treatises but cannot be ex- 
plained in detail in a botany 
for beginners. Besides the 
mode by formation of zodspores, 
as in the Protococcus, and that 
by the formation of zygospores, 
as in the desmids and in Spi- 
rogyra, there is a very interest- 
ing method which may be briefly 
outlined here, because it repre- 
sents an important principle 
in many kinds of reproduction, Fia. 196. — Common Bladder-Wrack or 
the union of fertilizing cells Rockweed, Mucus vesiculosus. (Re- 
with much larger egg-cells. This _ ted to about % the natural size.) 
fat at union is’ well) ilkis- b, air-bladders ; J, organs for produc- 
tion of spores. 
trated by one of the very com- 
monest of seaweeds, the common bladder-wrack or rockweed, 
Fig. 196, which grows on rocks between high and low water 
mark. It has many flat, leathery branches, which are buoyed 
up in the water by the air-bladders, 6. The spores are pro- 
duced by means of a rather complicated set of organs con- 
