COLEOCH&TE. 53 



ANNOTATIONS. 



This plant is one of the most complex of all Chlo- 

 rophyceae. The plant body is not filamentous as in 

 others, but the cells divide in two planes and remain 

 closely joined, laterally as well as endwise, thus forming 

 a flattened plate of cells one layer in thickness. Although 

 each cell of the plant usually contains chlorophyll, it 

 is evident that the lower side will tend to absorb most 

 materials from the substratum, while the upper side 

 is best placed for chlorophyll work; consequently we 

 have something like a division of labor between the dorsal 

 and ventral sides, though the plant is but one layer of 

 cells in thickness. 



Of the sex-organs the oogonium is more complex than 

 any seen before in that it has a long hair-like extension 

 from the bulbous base. This oogonium is not unlike 

 what we should have if the open end of the Vaucheria 

 oogonium should become narrow and long. The an- 

 theridia are small specialized cells formed on the tips 

 of marginal cells, which were originally nutritive. In 

 this respect the plant is less advanced than Vaucheria and 

 resembles Spirogyra, all of whose reproductive cells are 

 for a time nutritive. 



After fertilization the egg does not grow at once into 

 a new plant, but becomes encased by cells that grow up 

 around it, and passes through a resting period. After 

 the resting period the protoplasm of the oospore divides, 

 forming a number of zoospores (usually eight), each of 

 which can form a new Coleochate plant. Evidently, 

 therefore, we have a sort of alternation, since the 



