224 



MANUAL OF BOTANY 



those which soonest lose their motility, female. Plants with 

 such gametes are called heterogamous. 



In the lowliest Fungi, such as Mucoi; we have gametes pro- 

 duced in special branches of the mycelium {fig. 487). These 



are undifferentiated 

 Fig. -iSS. masses of protoplasm 



y^ which are never set 



free, but coalesce in 

 consequence of the 

 fusion of the cells in 

 which they are formed. 

 In plants which are 

 higher in the scale than 

 those mentioned we 

 find two kinds of 

 gametes distinctly re- 

 cognisable, which are 

 truly male and female. 

 As the habits of life of 

 these plants show so much diversity, we find a good deal of dif- 

 ference of structure of the gametes, which can be traced to the 

 environment and mode of life of the plants which produce them. 



Fig. 486. 



J^ig. 485. Part of a filameut of Ulothrix from wliicli 

 the gametes, fif, are escaping. (/', Free gamete, 

 f/", g\ Gametes coujugating. 



Fuj. 18(). Oonjugation in Spirogijra. Two filamentsare lying side by side, 

 and from cells opposite to each other protuberances are growing out to - 

 meet, a, a'. Each produees a gamete, b. When the protuberances have 

 met and fused, one gamete passes over and unites with the "other- c. 

 iL Adult zygospore. ' 



The male gamete in the Cryptogams which live under such 

 conditions that the coalescence of the sexual cells is brought 

 about through the medium of water, is generally a free swim- 

 ming piece of protoplasm, furnished with cUia or flagella like those 



