EVOLUTION AS SHOWN BY PLANTS 



349 



These last points, with reference to flowers, are not at 

 all easy to grasp outside of a laboratory course in the sub- 

 ject, despite the familiarity of the material discussed, and a 

 restatement of the points appears desirable. In connec- 

 tion with this study it is desirable to have a few complete 

 flowers, such as any of the lily type, available for use in 

 identifying and making perfectly concrete the points 

 referred to. 



Since stamens and carpels or pistils are sporophylls, 

 they, of course, bear the two kinds of sporangia: those 

 that produce microspores (pollen grains) and those that 

 produce megaspores. If stamens and carpels are sporo- 

 phylls, it follows that they cannot be sex organs, according 

 to the old notion, for they are structures that belong to the 

 sporophyte or sexless generation. 



The two gametophytes (male and female) in seed plants 

 are found just where they occur in all heterosporous plants, 

 namely, within the spores that produce them. The male 

 gametophyte, with its sperms, is within the microspore 

 (pollen grain). The female gametophyte, with its egg, 

 is within the megaspore. The sporangium that produces 

 the megaspore in seed plants has long been called the ovule, 

 and its greatest peculiarity is that it does not shed its spore. 

 Therefore, inside of the ovule is the megaspore, and inside 

 of the megaspore is the female gametophyte. It is no 

 wonder that the gametophytes (sexual plants) of seed 

 plants are seen only in the laboratory under the microscope, 

 and then only after special technic has made them 

 visible. 



The egg produced by the female gametophyte remains 

 within the ovule and is there fertilized, and there produces 



