232 



GENERAL BOTANY 



gamete. Many botanists hold that the female gamete secretes 

 some substance, such as cane sugar or an organic acid, which 

 attracts the male gamete to the female and thus insures 

 fertilization by directing the free motile male gamete to the 

 stationary egg. 



The zygote, or fertilized female gamete, remains in the female 

 gametangium (Fig. 121, a) and undergoes a period of rest. Dur- 

 ing this rest period it is protected by the old gametangium wall, 

 which remains in its former position around the egg cytoplasm. 

 The zygote is abundantly furnished with reserve food in the form 

 of oil and with the chloroplasts of the original 

 unfertilized female gamete. The germination 

 and growth of the zygote cell (6) to form a new 

 gamete plant is a com- 

 paratively simple process, 

 since the adult gamete 

 plant is unicellular and its 

 growth from the spherical 

 zygote cell consists mainly 

 in a great elongation of the 

 latter, with accompanying 



branching of the filament thus produced. During this elongat- 

 ing and branching process new nuclei and chloroplasts are 

 being formed by repeated divisions of the chloroplasts and con- 

 jugate nucleus of the zygote. The resulting gamete plant re- 

 sembles exactly the original mother plant, and in time, after a 

 period of vegetative activity, reverts to reproduction. 



Asexual reproduction. In Vaucheria sessilis another mode of 

 reproduction occurs which is asexual in its nature. In this 

 process the end of a filament swells up and becomes separated 

 into a distinct cell by a transverse cell wall (Fig. 122, a). 

 The cytoplasmic contents of the terminal cell then rounds up 

 and sends out minute cytoplasmic projections called cilia, thus 

 forming a large motile asexual naked cell, or zoospore (5). By 

 the rupture of the end of the enveloping wall this zoospore 

 becomes a free-swimming cell (<?), which later comes to rest and 

 grows into a new plant, clothed with a cell wall (Fig. 122, d, e). 



FIG. 121. Germination of the zygote 

 in Vaucheria 



a, zygote still attached to a filament ; 6, zygote 

 sending out a new filament 



