LIFE^HISTOEIES OF ALGM 243 



tips, i.e., dichoiomously (whence the n.a,rae 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 Phaeophyceae. 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 



