NATURE OF PLANTS 103 



the stigma, below which is an elongated stalk, the style, that 

 broadens out into a base or ovary. By longitudinal and trans- 

 verse sections of a pistil we gain a better idea of its real character 

 (Fig. 74, DF). The ovary is now seen t6 contain a cavity 

 from the walls of which one or more rather spherical bodies, 

 the ovules, are developed. The structure of the ovule is very 

 complicated. If a thin section is made through the center of 

 one of them it will be seen to contain usually but one large spore, 

 therefore called the megaspore (Fig. 76, mg). This spore is 



FIG. 75. Structure of the anther: A, diagram of the anther cut across, 

 showing the four cavities, sporangia (sing, sporangium), filled with spores. 

 B, cross-section of a mature anther. The tissue about the spores has 

 broken down, thus forming two cavities and at the left the breaking open 

 of the wall of the anther is shown. 



developed in a mass of tissue, the nucellus, and the whole is 

 surrounded by one or two coats, the integument, which grows 

 up from the base of the ovule but never quite surrounds it, 

 thus leaving a small opening or micropyle (Fig. 76, mi). The 

 megaspore, unlike the microspore, is never set free but is re- 

 tained permanently in the ovule. 



It is not known how the sporophylls have originated but there 

 are indications that they may have arisen through the modifica- 

 tion of leaves for the purpose of forming spores instead of con- 

 structing foods. It is for this reason that these organs are 

 called sporophylls, or spore-forming leaves, from phylon, a leaf. 

 Those forming small spores are sometimes called microsporo- 

 phylls instead of stamens and those forming large spores mega- 

 sporophylls instead of pistils or carpels. Very many mddifica- 

 tions of the sporophylls will be noted later in the work. 



52. The Germination of the Microspore and Megaspore. The 

 question now naturally arises as to the meaning of these peculiar 



