418 



VEGETABLE PHYSIOLOGY 



FIG. 164 ZOOSPOKE 

 Ulothrix. x 500. 



A feature of vegetative propagation which may here be 

 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 

 propagation of the individual, we meet 

 with two other methods of reproduc- 

 tion, both of which involve the pre- 

 paration 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 primi- 

 tive form, is afforded by the common 

 filamentous Alga Ulothrix. Any 

 protoplast of the filament can divide 

 A, closed ;B, ruptured, and j n o a num ber of separate pieces, 



allowing the zoogonidia m \ . , 



a to escape ; 6, mother- each of ovoid shape with a pointed 



cells of the latter, after . . .., 



escape of the zoogonidia end and furnished there with tour 

 cilia (fig. 164). 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 



