332 



REPRODUCTION IN PLANTS 



they give rise to the small but green and independent 

 gametophytes. The details of structure of the latter are 

 also shown in the illustrations. 



Heterospory is a term used by botanists to signify that 

 a plant produces spores of two different sizes (Fig. 87). 

 In most ferns the spores are all alike in size and give rise 

 indifferently to gametophytes of either sex or sometimes 



H1VD ■« 



Fia. 86. — The Gametophyt^ or sexual generation of the fern. 

 1. spores 2. a germinating ai>ore with a slender rootlet and a thicker 

 branch which will develop later intfl a flat sexual plant such as 

 3 and 4. 4. a sexual plant with antheridia (a), and rootlets or rhi- 

 zoids (r). At (sp) the spore is shown from which the whole has de- 

 veloped. .5. a part of a male sexual plant with two antheridia show- 

 ing the structure and method of discharging the mature sperms. 

 6. mature six»rms, 7. a female gametophyte with several female 

 sex organs (archegonia) on the under side and with a cluster of 

 rootlets. S a younger and older archegonium with an egg ready for 

 fertilization in the base of the older one. 9. a female sexual plant 

 (a) with a young sporophyte still attached to it. 



of both sexes. There are a few ferns, however, in which a 

 small spore is produced in one kind of sporangium and 

 gives rise to a male gametophyte so small that it can all be 



