42 



PLANT-LIFE 



usually chances that such a swarm will meet a similar 

 swarm recently liberated from another cell; in this 

 event marriage takes place with speed and minus the 

 overtures of courtship. The meeting gametes pair, first 

 becoming entangled by their cilia and spinning around 

 in a merry dance. The two bodies gradually fuse, and 

 in a few minutes the amorous partners have literally 



become one flesh. The 

 fused gametes now con- 

 stitute a spore, possessed 

 with four cilia. These 

 processes, however, are 

 speedily withdrawn into 

 the body of the spore, 

 and this product of the 

 marriage — really the 

 D r ' zygote — settles down 



Fig. 12.— Ulothrix zonata. and becomes attached 



A, Portion of filament, most of the cells to some object in the 



being empty ; gametes escaping from wa + e r 

 one cell ; B, biciliate gametes ; C, two 

 gametes conjugating ; D, young 

 zygotes ; E, ripe zygotes ; F, zygote j^ 

 developing after period of rest 

 G, zygote forming zoospores. 



It does not give 

 rise to a new filament ; 

 remains a one-cell 

 organism which absorbs 

 food, and consequently 

 grows for a few weeks. Its contents become gradually 

 denser and its wall thicker, until it is prepared and 

 furnished for a period of rest. The rest is taken in 

 summer, for Ulothrix takes its slack time in that 

 season ; it is most active through winter and spring. 

 Growth is arrested in hot weather, and the sexually 

 produced zygote is an ingenious device by means of 

 which the plant tides over the period of uncongenial 



