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of their branches together, as in C odium, or by cementing those 

 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 living in water, and all the larger forms 

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



Fig. 27t. 



Vaucheria sessilis. A = young sporangium. B= zoospore, with the spor- 

 angium from which it has escaped. C =a portion of the peripheral zone of a zoo- 

 spore. D = a young plant, with rhizoids, developed from a zoospore. (A , B, after 

 Gotz ; D after Sachs ; C after Strasburger.) (From Strasburger.) 



species float in water, some live on moist soil, exposed to the air. 

 But the members of the genus consist only of simple or branched 

 filaments, and when living aerially they lie procumbent. 



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 photosynthesis 

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



