GYMNOSPERMS 



439 



which, when young, are microspores; later their contents 

 become transformed into the male gametophyte. The 

 ovules contain megaspores, one of which develops the 

 female gametophyte ; the female gametophyte remains 

 within the ovule and produces eggs. By means of wind, 

 pollen grains reach the ovules. By means of pollen tubes 

 the sperms reach the eggs. Fertilization occurs. The fer- 

 tilized egg germinates. It develops an embryo, one for 

 each ovule. Meanwhile a hard coat called the testa has 

 formed about the ovule. This structure has now ceased 

 to be an ovule. It is a seed. The seeds are winged. 

 They escape from the ripe cones. Under favorable condi- 

 tions a seed germinates. A new sporophyte sprouts from 

 it. 



This life history may also be indicated as follows : — 



\ 



/ 



K. General Summary. — At this point it may be well to 

 review by summary the chief features of each of the great 

 groups. This is clearly done by the following quotation 

 from J. M. Coulter's Textbook of Botany. 



" Thallophytes. — Plants with a thallus body, but no 

 archegonia. 



Bryophytes. — Plants with archegonia, but no vascular 

 system. 



