GREEN ALGAE 3^5 



out (p. 140) how, as a set off against it, the more compUcated forms 

 of the Siphoneac have acquired additional meclianical strenijth, 

 either by internal cellulose ties, as in Caulerpa {Y\g. 333), or by matting' 

 of their branches together, as in Codium, or by cementing tho*«c 

 branches together, as in Halimeda. But these are concessions to 

 an essentially weak construction. It is only possible to carry it to 

 any considerable size when hving in water, and all the larger forms 

 are marine. Vanchevia is an exception : for though many of its 

 species float in water, some live on moist soil, exposed to liie .or. 

 But the members of the genus consist only of simple or br.uklK-d 

 filaments, and when living aerially they lie procumbent. 



I-IG. 333. 



Part of a transverse section of Caulerpa, showing the thick outer wall, .mil the 

 reticulate rods of cellulose, which act as ties, and give added rigidity. l-.O.B. 



( :< 50.) 



The cytoplasm of these plants contains many small chloroplasts. 

 and numerous nuclei usually lying internally to them. Centrally 

 is a large vacuole. In Vaucheria the product of photo-synthe.sis 

 appears as oil, but others of the Siphoneae may contain starch, which 

 is commonly present in Green Algae. The general physiology of a 

 coenocytic, or as it has been called a non-cellular plant, is probably 

 like that of any ordinary green plant. The difference lies in ihc 

 mechanical construction. 



Vegetative propagation is carried out in various Siphonaccous 

 Algae by non-motile, or by motile cells, produced in large numbers 

 in special branches, and liberated into the water. V\iucheria is an 

 exception, in that the whole contents of such a branch-ending, which 

 are previously shut off by a septum, are discharged as a single ciliated 

 zoospove, large enough to be seen with the naked eye. The escape is 

 effected in the early morning; after a period of movement the 

 zoospore comes to rest, and germinates directly into a new plant 



