112 



BOTANY 



Order V. Siphoneae 



Unlike the other Green Algae, most of the Siphonese are marine 

 plants, being especially abundant in the warmer seas. They are 

 characterized by the absence of vegetative cell-division, so that the 

 plant-body, which may often be of considerable size, is a tubular 

 structure, often extensively branched, but without any cross-walls, 

 and all parts of the internal cavity are in direct communication. 

 The cytoplasm lines the interior of the tubular thallus, and in it 

 are imbedded numerous nuclei and small chromatophores. It is 

 doubtful whether the plant-body of the Siphoneae can properly be 



A 



ri 



FIG. 83. A, S, Mesocarpus sp.: cells showing the single axial chroma! ophore. 



B, seen from the side; n, nucleus. The small round bodies are tannin vesicles. 



C, zygospore of Mesocarpus sp. (x 200). D, E, Gonatonema sp., showing aplauo- 

 spore, sp (X 450). 



considered a single cell, as is sometimes done. It seems better to 

 look upon it as a " coenocyte " a cell complex, in which the division- 

 walls are suppressed, and the protoplasts confluent. 



The Plant-body. One of the simplest members of the order is 

 Botrydium (Fig. 84), a plant which is sometimes extremely abundant 

 growing upon wet clay. The plant consists of a pear-shaped, dark 

 green vesicle, about one-half millimetre in diameter, which is fastened 

 into the earth by a system of dichotomously branched colorless roots. 

 A microscopic examination shows that all parts of the interior of the 

 plant are in open communication. The cytoplasm lines the wall as a 

 thin layer, in which may be demonstrated many small nuclei. The 



