FERNWORTS AND SEED-PLANTS. 57 



14. Boil a leaflet for a minute in water. With a needle turn back a 

 flap which covers the spore cases; observe that it is a specialized portion 

 of the edge of leaflet. 



15. On the under side of the flap a mass of yellowish spheroidal bodies, 

 the spore cases. Scrape away most of them and notice the relation of 

 their points of attachment to the veins. 



Mount some of the spore cases and observe 



16. Their shape ; the stalk by which they were attached. (Fig. 236. ) 



17. The darker ridge, annulus, which serves to burst them when ma- 

 ture. (Fig. 236.) 



18. Study the manner of bursting. Tear a bit of indusium from a dried 

 specimen previously soaked in water, removing most of the sporangia. 

 Allow it to dry while watching it with a lens, illuminating from above. 



19. Demonstration. Mount sporangia and spores and show their 

 structure, especially the annulus. 



Seed-plants. 



67. Development. — Among the highest plants, those 

 which produce seeds, the differentiation of the body is essen- 

 tially the same as in fernworts. The alternation of sexual 

 and non-sexual phases is still traceable, though greatly 

 obscured by the extreme reduction of the gametophyte. 



This tendency to the reduction of the sexual phase, which was re- 

 marked in passing from the mossworts to the fernworts, continues, until 

 in the highest seed-plants the gametophyte is wholly microscopic. 

 Even by the aid of the microscope, it is possible to identify only the sex- 

 ual organs which it produces, and one or more cells which are, perhaps, 

 the rudiments of its vegetative body. 



The sporophyte, consequently, is the only phase of the 

 seed-plant visible to the unaided eye. 



The body of the sporophyte exhibits the same members, 

 viz., stem, root, and leaf, having the same general form, and 

 subject to the same modifications, as in the fernworts. An 

 account of the vegetative members of the fernworts and seed- 

 plants occupies the following three chapters. 



