222 



MANUAL OF BOTANY 



In the Angiosperms there is no archegonium, and a single 

 oosphere hes free in the cavity of the spore {fig. 484, oos), being 

 hardly distinguishable from the other cells which are near 

 it. After fertihsation in these plants, the gametophyte under- 

 goes a further development, the cavity of the spore becoming 

 filled by a tissue bearing the name oi endosperm. This is, how- 

 ever, not morphologically comparable to the tissue bearing 

 the same name in the Gymnosperms, which is developed before 



Fig. 4.'^2. 



arch. 



Fhj. 482. Germination of megaspore of ^elaginella. After Pfeffer. 

 ardi. Archegonium. pm, fni'. Young embryos. 



differentiation of the sexual cells, and is morphologically the 

 same structure as the prothallium of the higher Cryptogams. 



T/ie Gametes. 



The gametes show a great deal of variety of form, size, and 

 degree of differentiation. In the lowliest Algse they are not very 

 different in appearance from the zoogonidia which the same plants 

 produce, and are liberated in large numbers from the cells in 

 which they originate {fig. 485). They are somewhat pear-shaped 

 masses of protoplasm, without any protective coat, and furnished 

 with two long tails or flagella of protoplasm, which spring from 

 the narrow end of each mass. By means of these they are 

 capable of movement in the water in which the plants exist. 



