178 GENERAL BIOLOGY 



the " plant," the gametophyte being a minute de- 

 pendant upon it. 



In the seed plants there always occur the two 

 kinds of spores, megaspores and microspores. 

 The latter are more often known by the more familiar 

 term pollen. In some species of plants both are 

 borne on the same plant (monoecious type) ; in others, 

 each is developed on a different plant (dioecious type) . 



The leaves which bear the microsporangia are 

 called stamens, those that bear the megaspores, 

 carpels. Both these forms of metamorphosed leaves 

 are usually surrounded by other, highly modified, 

 frequently colored leaves (petals, sepals), to form a 

 flower. When the carpels grow together in a mass, 

 as is frequently the case, we speak of it as the pistil. 



The carpels bear sporangia, to which the name 

 ovule has long been given, although it must not be 

 forgotten that they are not " eggs," but are developed 

 by the sporophyte, the asexual generation. The 

 megaspore is never released from the sporangium, 

 and the sexual generation begins its existence there. 

 On the other hand, the microspores (pollen) are 

 matured in great numbers in the sporangia of the 

 stamens, and, when released, are carried by the wind, 

 insects, and other agents to the sticky termination of 

 the pistil (the stigma). When one sticks here, it 

 begins to sprout and grow, much as moss-spore on 

 damp ground. Since, in the flowering plant, however, 

 the megaspores are inside the carpels and are never 

 released, the pollen spores must grow down into the 

 carpel to them. This it does in the form of a (rela- 



