22 PLANT LIFE. 



the basal cell is elongated and pointed, and is colorless, 

 because it is not furnished with chloroplasts like the others. 

 By this pointed cell the plant is loosely attached, at least 

 when young, to the substratum, while the green portion 

 waves freely in the water. Thus arises a distinction into two 

 parts, viz., the r/iizoid and the thallus. 



In Cladophora, Vaucheria, and their allies, the plants are 

 generally attached by a well-developed rhizoid-region, which 

 is often branched (w, fig. 28), as is also the thallus. In 



Fig. 28. — A young plant of Vaucheria, developing from the spore. A, mature 

 spore ; B, the same after germination has begun ; C, plant further developed from 

 spore, s/, with growing apex, j, and rhizoid, «/, by which it attaches itself to the 

 mud. The chloroplasts are numerous and close together next the wall on all sides. 

 Magnified 28 diam. — After Sachs. 



contrast with the preceding, therefore, localization of growth, 

 producing branching, may be observed. 



27. Branching. — A branch begins by the growth in area 

 of a limited portion of the cell-wall. The pressure of the 

 contained protoplasm upon the wall causes it to bulge out- 

 ward at this point, and the convexity gradually increases as 

 the region grows until the swelling becomes an outgrowth, 

 whose further lengthening constitutes a branch similar to the 

 main filament. Growth in length may be limited to the tip 

 of the filament, or to a narrow zone including one or more 

 cells, or it may occur indifferently in any part. 



28. Coenocytes. — Many algae, while externally like others, 

 which are divided into true cells, have not the units of 



