392 



GAMETOPHYTE OF ANGIOSPERMS 



archegonia are developed at the very start of the gametophytic 

 growth. The nicety of such a sequence of development is alto- 

 gether admirable. In the ferns, if fertiHzation is not effected, 

 the prothallial growth is wasted, but in the angiosperms there is 

 no prothallial growth without fertilization. 



The male gametophyte presents several features suggestive of 

 the gymnosperms. The germination of the microspores usually 

 begins within the sporophylls, and by the time that they are shed 

 and carried to the stigma, their nuclei have already divided once 

 and each spore consists of a large tube cell and an antheridial cell 

 (Fig. 272, B). There is very rarely a trace of the vegetative 



Fig. 272. Germination of the microspore: A, mature microspore of lily, 

 B, first stage of germination — t, tube cell; a, antheridial cell. C, final divi- 

 sion, in this case effected while in the microsporangium — /, tube cell; a, an- 

 theridial cell forming directly two male gametes. D, diagram showing the 

 formation of the tube which grows down the style and finally reaches the 

 female gametophyte. The two male gametes, g, are shown passing down 

 the tube; /, tube nucleus. All the figures in sectional view. 



cells of the gametophyte, as in the cycads and pines, since the 

 necessity for these cells no longer exists. The stigma is generally 

 provided with minute outgrowths or papillae derived from the 

 epidermal cells which serve to hold the microspores (Fig. 269, s). 

 These cells of the stigma usually secrete a sugary solution which 

 nourishes the microspores and causes a continuation of their ger- 

 mination. It is noteworthy that these microspores may be made 

 to germinate by placing them in sugar solutions, but the approxi- 



