REVIEW OF THE GREEN ALGJE 251 



red snow plant (H&matococcus). The plant is a single cell. It 

 multiplies by division into two plants which are associated in the 

 parent envelope but a short while, when they escape and become 

 independent. In such a plant as Pleurococcus the cells are united 

 for a longer period during multiplication, while in the colony 

 algae like Pandorina, and the water-net, the individuals are 

 permanently united in a loose association. Most of the desmids 

 are single-celled plants, but other members of the conjugating 

 algae are filamentous. They are, in reality, colony algae, since 

 each cell of the thread is identical in structure, and capable of the 

 same functions; each cell is capable of division and growth, 

 growth not yet being localized at any definite growing point, or 

 area. In the filamentous algae (Confervoideae), however, while 

 the cells are nearly all alike, growth is localized, either at the 

 tips of the threads and branches, as in Cladophora and Choeto- 

 phora, or in definite cells at any point in the thread, as in (Edo go- 

 mum. Many of the filamentous forms are branched. This 

 produces a more complex plant body. In some forms the 

 branching is so close and compact as to approach tissue masses 

 in the cushion-like mats or spheres of some species of Coleochcete 

 and Chatophora, or to form definite leaf -like cell plates, as in the 

 sea lettuce and the shield coleochate. 



386. Differentiation of sexual organs.* In the low,er green 

 algae, the one-celled forms (Protococcoideae) and the conjugating 

 algae (Conjugatae), the gametes are usually equal in size, though 

 in some forms there is a distinct difference, the male, or sperm 

 cell, being smaller than the female, or egg cell. This is true in 

 many of the filamentous algae (Confervoideae) where both gametes 

 are motile cells. In forms like (Edogonium, and Vaucheria 

 among the siphon algae (Siphonales) , definite and distinct organs 

 are developed the sex of which can be recognized. The female 

 organ, the egg case (oogonium), is large and contains a single 

 large egg with an abundance of cytoplasm to furnish nutriment to 

 the germinating egg. The male organ, the sperm case (antherid- 

 ium), is smaller in size, but develops usually a very large num- 



* For reference, or special assignment. 



