4 A TEXT-BOOK OF BOTANY. 



nutritive cells of the plant are involved in the process it is some- 

 times spoken of as vegetative multiplication. 



In both lower and higher plants, with the exceptions just 

 noted, reproduction is also earned on by means of spores. 



Fig. s. Ulothrix zonata. A, young filament with rhizoid cell (r); B, piece of filament 

 showing escape of swarm spores; C, a swarm spore or zoospore with 4 cilia; D, biciliate 

 gametes escaping from a filament; E, F, G, showing difi'erent stages of union of two gametes; 

 H, young zygote or zygospore in which the cilia have been absorbed; J, i -celled plant 

 developed from zygote; K, young plant organizing zoospores. — After Dodel-Port. 



Depending upon their origin two classes of spores are distin- 

 guished, namely, (a) asexual spores, and (b) sexual spores. In 

 the production of asexual spores the contents of a certain cell 

 called a mother cell or sporangium break up into a number of 

 new cells sometimes called daughter cells, which escape through 

 the cell-wall. In the lower plants, particularly those growing 



