404 THE EVOLUTION OF THE SPOROPHYTE 



and depend upon food stored in the megaspores by the previous 

 sporophyte generation. 



The spermatophytes added the final stages in the evolution 

 of the sporophyte, as follows : 



Seventh. The ovule arose through the retention of the mega- 

 spore (embryo sac) in the megasporangium (nucellus) inclosed 

 by integuments. The development of the embryo sporophyte 

 within the embryo sac, and the ripening of the ovule, produced 

 the seed. 



Eighth. The ovule case, or ovary, appeared with the devel- 

 opment from one or more megasporophylls, or carpels (frequently 

 with adjacent tissue), of an inclosing structure, the pistil, upon 

 which was differentiated a special region, the stigma, for the 

 reception of the pollen. 



Ninth. The stamen was developed from the microsporo- 

 phyll. 



Tenth. Complicated flowers arose by various groupings of the 

 carpels and stamens, together with showy or protective envelopes 

 constituting the perianth. 



Eleventh. The flower cluster, or inflorescence, appeared, culmi- 

 nating in the composite head. 



Twelfth. The tissues of the spermatophytes became more com- 

 plicated in many respects than those of the pteridophytes. 



376. The degeneration of the gametophyte. Many steps in 

 the degeneration of the gametophyte were closely related to the 

 advances of the sporophyte. 



In most of the bryophytes the gametophytes appear as 

 organisms equally complex with the sporophytes, and in many 

 forms they are more complex. Thus the gametophytes of the- 

 mosses and leafy liverworts show a considerable advance over 

 the thalloid gametophytes of the simple bryophytes. The thal- 

 loid gametophyte, however, seems to have been the type that 

 was passed over to the pteridophytes, and Anthoceros probably 

 gives a fair idea of the relative complexity of the two genera- 

 tions at the time when the first pteridophytes arose. 



