348 NATURE STUDY AND AGRICULTURE 



pollen. The carpels, usually united to form the organ 

 known as the pistil, are another kind of sporophyll; they 

 bear the megaspores, and the megaspores are commonly 

 known as nothing at all because they are never seen. This 

 is due to the fact that they never are discharged from the 

 sporangium which bears them. This sporangium forms 

 most of the structure commonly known as the ovule. 



Having noted that the state of producing two kinds of 

 spores is called heterospory, we can see, for the sake of 

 clearness, that the state of bearing two kinds of sporophylls, 

 each of which bears a kind of sporangium different from 

 that borne by the other, might be called heterosporophylly. 

 As a matter of fact that cumbersome word is not used, but 

 the fact which it names needs to be made clear, and is ex- 

 emplified by stamens and carpels. 



Also, having noted that in heterosporous plants the 

 generations which result from the germination of the spores, 

 that is the gametophytes, are ingrowing within the spores 

 and parasitic, we now need to note that the next step in 

 this direction is the case of the ovule cited above. That 

 is, the megaspores were said to have no common name 

 because they are never seen under ordinary circumstances; 

 they are retained within the ovules which bear them, and 

 there the male generation or pollen tube, bearing the sperms, 

 goes in search for the eggs which have developed in the 

 internal, parasitic female gametophyte inside the mega- 

 spore. Thus we have here, added to the retention of the 

 gametophyte within its mother spore, the retention of the 

 spore itself within its mother sporangium, and with the 

 arrival of this step in evolution we have the arrival of that 

 great epoch-marking habit in plants: the seed habit. 



