THE ALG^E 



131 



their bases are concealed. Similar cryptostomata have been found 

 in some of the Phaeosporeae. 



In Sargassum (Fig. 102) and Cystophyllum the much-branched axis 

 has attached to it numerous leaflike appendages, so that the appear- 

 ance of the plant is much like that of the ordinary terrestrial Flower- 

 ing Plants. Where air-vesicles are present they may be buried in 

 the thallus, as in Fucus 

 vesiculosus (Fig. 101, A), 

 or are borne upon short 

 lateral branches, as in 

 most species of Sargassum 

 (Fig. 102). 



Apical Growth. Growth in 

 the Fucacese is apical and due 

 to the division of a single large 

 apical cell. This in Fucus is 

 situated at the bottom of a little 

 pit at the end of the branches. 

 The cell here (Fig. 103) has the 

 form of a truncated wedge, 

 whose outer face is oblong, the 

 long axis being at right angles 

 to the broad surface of the 

 branch. Segments are cut off 

 from the lateral pieces, and also 

 from the inner truncate edge. 

 The young segments divide 

 rapidly and produce a mass of 

 small-celled tissue surrounding 

 the apical cell. These cells gradually pass into the tissues of the older parts. 



The tissues of the mature parts closely resemble those of the Kelps. There 

 are several layers of small cells joining the outside tissue, and these contain most 

 of the chromatophores. The inner cells are elongated, and their cell-walls are 

 highly gelatinous. Sieve-tubes may also be present. 



Reproduction. None of the Fucaceae develop zoospores, but small 

 pieces of the plant may become detached and form new individuals. 



The sexual organs are antheridia and oogonia, borne in pits much 

 like the cryptostomata, of which they are probably modifications. 

 These conceptacles are usually formed upon somewhat modified por- 

 tions of the plant-body. In Fucus the fertile branches have their 

 ends very much enlarged, and in Sargassum there are special fertile 

 branches developed. The position of the conceptacles is indicated by 

 papillae. Antheridia and oogonia may be formed in separate con- 

 ceptacles (in different plants) as in Fucus vesiculosus and Halidrys ; 

 or they may be borne in the same conceptacle (Fucus fastigiatus). 



Antheridium. The antheridia in Fucus (Fig. 104, D, E) are small oval cells 

 borne at the ends of branches of some of the hairs within the conceptacle. They 



FIG. 102. Sargassum sp. ; v, air-bladders. 

 (About natural size.) 



