THE BROWN ALG 485 
grows into a sexual plant like the one already described. Thus in 
the life-history of Coleochzete a sexual form producing gametes, 
alternates with a form of plant which produces only non-sexual 
spores. That which bears gametes is termed the gametophyte,1 
while the merely spore-bearing one is the sporophyte.2_ Each repre- 
sents a generation; hence the plants whose life-history is thus di- 
vided are said to exhibit an alternation of generations. 
175. The brown alge (Class Pheophycez) are charac- 
terized in general by a brown coloring matter, phycophein,' 
masking the chlorophyll. They are almost entirely marine. 
Besides many comparatively simple forms there are some 
showing a remarkably high development of the vegetative 
system. 
In their methods of reproduction the brown alge present rather 
close parallels to various chlorophyceous types, very rarely, however, 
exhibiting an alternation of generations. 
One of the commonest genera is Laminaria (Fig. 316) 
which includes the familiar leathery ‘“‘sea-tangles,”’ “‘kelps,”’ 
or “ Devil’s aprons” often cast upon beaches after a storm. 
The thallus consists of a flat, more or less leaf-like part 
(pseudo-leaf) attached to a stalk (pseudo-stem) at the base of 
which is a hold-fast (psewdo-root), often much branched, which 
clings to stones or other means of anchorage on the bottom. 
This thallus which may be yards in length consists of an exceed- 
ingly large number of cells among which a considerable differ- 
entiation may be observed. Thus in the stalk as shown in 
Fig. 317 we have an outer group of cells forming’ a sort of rind 
(r, r) which is comparatively tough and thus protective, while 
at the same time it serves as a food-making part since the 
cells are rich in chlorophyll. ‘Those inclesed by the rind, 
(p, p) form the chief bulk of the stalk, are pale in color, and 
serve largely for the storage of food-materials elaborated 
by the outer cells. In the rind occur numerous cavities 
(g, g) filled with a mucilaginous material. The pseudo-leaf 
shows a differentiation of cells similar to that of the stalk. 
For the most part as soon as they are formed the cells lose 
the power of dividing; but in the region where the pseudo- 
1 Gam’et-o-phyte < Gr. gametes, spouse; phyton, plant. 
2 Spor’o-phyte < Gr. spora, spore. 
3 Phy’’co-phe’in < Gr. phycos, seaweed; phaios, brown. 
