108 



FOUNDATIONS OF BIOLOGY 



as the ANTHER. Within the anther POLLEN GRAINS are 

 formed. The pollen grains are microspores and, therefore, it is 



FIG. 59. Transition between petals and stamens in a Water Lily. (After Gray.) 



apparent that 



FIG. 60. Dia- 

 gram to illustrate 

 the method of union 

 of three carpels 

 ( megasporophylls ) 

 to form the ovule 

 case of a pistil 

 (compound) . The 

 edges which unite 

 form the point of at- 

 tachment of the ov- 

 ales. (After Gray.) 



the pollen sacs of the anthers are MICROSPORAN- 

 GIA and the stamens are microsporophylls. 



Finally, just within the circle of stamens 

 is the fourth whorl of floral leaves, the car- 

 pels, in which specialization has gone so far 

 that practically no suggestion of leaf struc- 

 ture remains. Each carpel consists of three 

 parts: a lower, expanded portion termed 

 the OVULE CASE, merging above into the 

 elongated, slender STYLE, the tip of which is 

 the STIGMA. Such a fully developed carpel 

 is known as a PISTIL and when, as frequently 

 happens, the various carpels fuse to form a 

 composite structure, this is termed a com- 

 pound pistil. Within the ovule case are de- 

 veloped the reproductive bodies known as OV- 

 ULES which are essentially MEGASPORANGIA, 

 for within each is formed a megaspore, com- 

 monly known as an EMBRYO SAC. A carpel, 

 therefore, is a megasporophyll. (Fig. 60.) 



