ORGANS OF REPRODUCTION. 



381 



simplest plants of this sub-order, as Protococcus or Palmella 

 {figs. 1 and 2), consist of a single cell, so that the mitritire and 

 reprodiictive processes cannot be separated ; but each cell has 

 the power of dividing by the process of cell-division (see Cell- 

 division) into two or four new cells, from which new individuals 

 are formed when the parent-cell bursts. (See Gonidia of Lichens, 

 p. 377-) In other cases, as in Zygnema {fig. 831), the cells of 

 two filaments, c, d, unite by a lateral cellular process, p, by 

 means of which their contents {endochrome) intermingle, and the 

 result is the formation of a spore, s, termed an oospore, capable 

 of germinating. This process is called conjugation, and will 

 be more particularly explained hereafter. In other plants of 

 this group the spore is apparently developed without conjuga- 

 tion. Besides these true spores, which may be called resting 

 or inactive spores, we have also formed in the plants of this 

 group, as in many other Algae, what have been called zoo- 

 spores or gonidia {fig. 832). These are formed apparently 

 without any process of fertilization out of the contents of the 

 cells, and are discharged, according to Henfrey, withoxit any 

 cellulose coat, but consist simply of a protoplasmic sac. They 

 are fvu'nished with cilise, by which they are enabled to move 

 freely for some time, hence their name ; but they afterwards 

 settle down and germinate, when they also acquire a cellulose 



Fig, 833. 



Fig. 831. Portions of two filaments of Zygnema conjugating, c, d. Tlie 

 contents (e7idoc/irow!e) of two cells mixing by means of alateral process, 

 ■p. s. Germinating spore (oo-spore),\vliicii results from tlie union and 

 mixing of the contents. Tiie two cells below contain spiral filaments. 



i^tsr. 832 Zoospore of CVioctoi^/iorM, consisting of a cell, i^, with four 



ciliag, c, at its apex. Fig. 833. Erid of a lllament of Vaacheria Ungeri, 



with a siiigle gonidium or zoospore, g, escaping. 



coat. The number of cilise varies in different plants ; in some 

 there are two {fig. 30), in others four {fig. 832), in others 

 there is a tuft of cilise at one end {fig. 31), while in others, again, 



