318 THALLOPHYTES 
a form with a small balloon-shaped plant body, which is commonly 
found projecting from moist soil, there are no sex organs and the 
gametes are alike. 
The Siphonales are most peculiar in having a tube-like plant 
body. In the production of well-defined sex organs they show 
considerable advancement in sexual reproduction. 
Summary of Green Algae. — In having chloroplasts and well- 
defined nucleus and cytoplasm, the cells of the Green Algae are 
more advanced than those of the Blue-green Algae. In the 
simplest forms the plant body is a single cell, either motile or 
non-motile, and the uniting of cells into colonies is a prominent 
feature. In the higher forms the plant body is multicellular and 
in the form of a filament or disk. The multicellular forms have 
not only established the habit of cells living together to form a 
complex plant body but have also to some extent differentiated 
cells. These habits look forward toward the formation of plants 
consisting of a countless number of cells, which are differentiated 
into tissues, such as occur in the higher plants. They introduced 
sex cells which were at first alike, and later differentiated the sex 
cells, thus introducing eggs and sperms, the sex cells of the higher 
plants. They also introduced sex organs which are prominent 
structures in the Mosses and Ferns. 
Brown Algae (Phaeophyceae) 
These Algae are marine forms, occurring on all sea coasts but 
more abundantly in the cooler waters. They have two pigments, 
chlorophyll and a brown pigment called fucoxanthin, but the 
brown pigment obscures the green one and determines the color 
of the plant. Both pigments probably help in the manufacture 
of food, although the exact function of fucoxanthin is not known. 
These Algae grow anchored by holdfasts to the rocks and their 
bodies are so tough and leathery that they are not injured by the 
beating of the waves. 
Although a few are simple filaments, most of them are much 
more complex than any of the Green Algae. The plant body of 
the majority of them not only consists of a greater number of 
cells, but there is more differentiation among the cells than in the 
Green Algae. In the largest of them the plant body often attains 
a length of several hundred feet. As shown in Figure 274, the 
