26 A TEXT-BOOK OF BOTANY. 



fast (Fig. n). It occurs in meadow pools or ponds, frequently 

 in streams attached to rocks near rapids. The cells are somewhat 

 elongated and contain a large, irregular chromatophore with 

 pyrenoids. Most of the cells are vegetative cells, interspersed 

 among which are the cells producing the spores. Zoospores are 

 produced singly in the cells and are provided with cilia at one 

 end. After swimming about for some time they attach themselves 

 at this ciliated end to a substratum and develop into filaments. 

 Two other types of cells are formed and which give rise either 

 to ougonia, the female organ containing a large egg cell, or to 

 antheridia, the male organ containing many sperms. The union 

 of a sperm with an egg cell produces an oospore with a very thick 

 wall, capable of over- wintering and developing again when con- 

 ditions are favorable. 



THE C 1 1. \RACK.E, or Stoneworts, is a highly differentiated 

 group that is considered as a distinct class between the Chloro- 

 phyceae and the Phaeophyceae. They stand so entirely by them- 

 selves that many authorities do not consider them as even Algae. 

 They consist of jointed stems, from the nodes of which whorls of 

 from 4 to 10 leaves are developed, and these bear the sexual 

 organs (Fig. 13). In many of the members of this family the cell- 

 wall is incrusted with lime salts. Chara occurs in great masses 

 in the bottom of ponds and shallow lakes. It occurs in sufficient 

 quantity in many places so that the body of water has a distinct 

 orange color, due to the immense numbers of antheridia. The 

 plant is of such luxuriant growth that if single individuals are 

 kept in an aquarium or large glass vessel it will greatly multiply 

 during the winter and persist for many years. In ponds where 

 ( hara occurs larjje quantities of lime are deposited, so that in 

 ancient deposits now exposed to view one often finds imbedded 

 therein the remains of the spore-fruits. 



In the luiuj cells or intcrnodes there is a large vacuole and 

 a thin layer nf protoplasm containing a central nucleus and a 

 la rue number of oval or lens-.^haped chromatophores. In some 

 forms. especially in Xitella. the inner protoplasmic layer shows 

 a streaming mo\ement. This is very interesting, as a distinct. 

 streaming movement does not occur in most plants and is limited 

 to a few water plants, the staminal hairs of Tradescantia, the leaf 



