LIFE HISTORIES OF ALG.E 243 
tips, i.e., dichotomously (whence the name dichotoma) , but 
showing no differentiation into anything like stem and 
leaf. One end of the plant is differentiated into a special 
branching organ, the hold-fast, by which it becomes 
attached to rocks, shells, and other convenient solids. 
As in Fucus, again, the green chlorophyll is masked by a 
brown pigment, which indicates the relationship of the 
plant to the Brown seaweeds, or Phaeophycese. There are 
two kinds of branches cylindrical ones which are sterile, 
and others more strap-shaped, or ribbon-like, which 
eventually bear the reproductive organs. 
Vegetative multiplication may occur by the separation 
of portions of the thallus, which may become established as 
independent plants. In some species of Dictyota, specially 
differentiated bodies have been noted, resembling the 
brood-buds or gemmae, such as occur in some of the liver- 
worts and mosses. 
229. Reproduction. With reference to reproductive 
organs, three kinds of plants occur: 
1. Plants bearing asexual spores only (asexual). 
2. Plants bearing oogonia only (female). 
3. Plants bearing antheridia only (male). 
But the most interesting feature in this connection is that 
the plants of all three groups look very much alike, except, of 
course, for their different kinds of reproductive organs, 
and for unimportant individual variations. 
Oogonia and antheridia are both produced from surface 
cells. The surface cell first divides into a smaller stalk- 
cell, and a larger external one, rich in protoplasm, which 
forms the gametes. The protoplast of the oogonium does 
not divide, as in Ascophyllum and Fucus, but develops 
into only one very large egg; while the protoplast of the 
