342 A TEXTBOOK OF GENERAL BOTANY 
Chlorophyceae, exhibit a great variety of forms (Fig. 354). 
Reproduction is either by asexual spores or by the fertilization 
of female cells by male cells (Fig. 355). Unlike the male cells 

Fig. 354. Red alge 
Upper left, Chondrus crispus; upper right, Por- 
phyra; lower left, Polysiphonia violacea; lower 
right, Corallopsis salicornia 
of other algz, those 
of the Rhodophyceae 
are not motile but 
are transported by 
the movement of the 
water. 
Economic impor- 
tance of alge. ‘The 
direct economic im- 
portance of alge is 
comparatively slight. 
Some of the seaweeds 
are used as food in ya- 
rious countries, the 
collection of them 
for food being an im- 
portant industry in 
Japan. The larger 
brown algz serve as 
sources of potash and 
iodine. Agar, used as 
a medium for grow- 
ing bacteria and also 
aS a medicine, is ob- 
tained from red alge. 
Certain of the brown 
and red alge are used 
as medicine. Fossil diatom shells (Fig. 350) are the basis of many 
cleansing preparations which cleanse by their scouring action, 
while dynamite is nitroglycerin absorbed in diatomaceous earth. 
Although the direct importance of alge is not great, they are 
indirectly of tremendous value as the ultimate source of the food 
of fishes. 
