158 BOTANY. 



leaves, is the type of the family Ulvacem. It reproduces 

 by zo5spores. The plant is composed of two layers of 

 cells, and in any of these, by internal cell-formation, zoo- 

 spores may be produced; these escape into the water, 

 where they swim about by means of their cilia, after a 

 time coming to rest and developing directly into new 

 plants, or conjugating and forming resting-spores. 



279. The common Conferva { Ulotrichiacem) of our 

 watering-troughs and fountains, consists of slender un- 

 branched threads which are attached at one extremity by 

 a colorless "root-cell." Their reproduction is very much 

 like that of the Sea-lettuce, any cell being capable of 

 forming zoospores (Fig. 86, B). 



280. In the common Water-flannel ( Oladoplwrci) of our 

 creeks and rivers we have a good example of the family 

 GladoplioracecB. It is a large, dark green, much-branched 

 plant, which attaches itself to stones and timbers in the 

 water. It grows so vigorously that it soon forms long 

 matted masses, often several metres in length, which float 

 and wave back and forth in the currents of water. It pro- 

 duces myriads of zoospores. 



281. Family Oedogoniaceae. — The plants constituting 

 this family are composed of articulated, simple, or branched 

 filaments, which are attached to sticks, stones, earth, or 

 other objects by root-like projections of the basal cells. The 

 cells are densely green throughout. They inhabit ponds 

 and slow streams, and form green or brownish masses which 

 fringe the sticks and other objects in the water. 



282. The asexual reproduction of Oedogoniacese is very 

 curious. During the early and active growth of the plants 

 the protoplasm of certain cells escapes as a large zoospore 

 (Fig. 87, ^ and B); it is provided with a crown of cilia 



