KEPBODUCTION 



427 



FIG. 164. ZOOSPOEE OF 

 Ulothrix. X 500. 



emphasised is that the new individual is developed con 

 tinuously after its origination. There 

 is no resting period, such as we find 

 in most cases, to mark the behaviour 

 of the more specialised reproductive 

 cells to be discussed below. 



Apart from cases of vegetative pro- 

 pagation of the individual, we meet 

 with two other methods of repro- 

 duction, both of which involve the 



preparation of special cells set apart for this purpose. The 

 first of these is characterised by the fact that each cell so 

 produced is able to grow, either at 

 once or after a short period of rest? 

 into a new plant, which may or may 

 not be exactly like the one from 

 which the reproductive cell was 

 formed. In plants exhibiting the 

 simple organisation which we find 

 among the seaweeds and the fungi, 

 the parent and the offspring are in 

 most cases precisely similar. The 

 difference in this respect between 

 them and plants higher in the scale 

 will be discussed a little later. A 

 good example of this mode of repro- 

 duction, which was probably the 

 primitive form, is afforded by the 

 common filamentous Alga Ulothrix. 

 Any protoplast of the filament can 

 divide into a number of separate 

 pieces, each of ovoid shape with a 

 pointed end and furnished there with 

 four cilia (fig. 1 64) . These new proto- 

 plasts swim about for a time in the water, then come to 

 rest, and after a time grow out into new filaments. Not 

 only the Algae but the Fungi afford examples of the 



FIG. 165. Two Gosi- 

 DAJSGIA os 1 AcUya 



A, closed ; B, ruptured, and 

 allowing the zoogonidia a to 

 escape ; b, mother-cells of 

 the latter, after escape of 

 the zoogonidia from them. 



