324 



PRACTICAL BOTANY 



298. The carpel, megaspore, and female gametophyte.i The 



carpel or pistil consists of three parts : the enlarged base which 



is the ovary, 

 one, several, 

 are 



ovules 



m which 



or many 



borne : the 



elongated portion above 

 the ovary, the style; at 

 the tip of the style, the 

 stigma, which in different 

 plants is divided or ex- 

 panded in various ways 

 (Figs. 110 and 111). 

 When ripe, the stigma 

 secretes a sticky fluid, 

 or produces a coating 

 of hairs by means of 

 which pollen grains are 

 caused to adhere to it. 

 The style, which may 

 have lifted the stigma 

 into an exposed position, 

 now serves as tissue 

 through which pollen 

 tubes may grow to the 

 ovules. The ovary con- 

 tains a special cavity in 

 which ovules are borne 

 in a variety of positions 

 (Fig. 102). The ovule 

 may be upright or more 

 or less recurved toward 

 its base. The surface of 

 the ovule consists of one 

 or two integuments, which at the tip do not quite cover the 

 inner tissue. This open tip is the micropyle. Similar structures 

 ' See footnote at beginning of the chapter on Gymnosperms. 



Fig. 265. Diagram of the ovule of an angi- 

 ospermous plant, showing the parts of the 

 ovule, the outer integument (oi), the inner 

 integument (i), the micropyle which is the 

 opening between the parts of the inner in- 

 tegument, and the pollen tube which has 

 grown through the micropyle 



In the interior of the ovule is the embryo sac, 

 within which are the tip of the pollen tube, the 

 egg and a sperm in process of uniting. Near the 

 egg are the two synergid cells, in the center of 

 the sac are the two embryo sac cells and the 

 other male cell, which unite to form the endo- 

 sperm cell, and at the end of the sac are the an- 

 tipodal cells, which usually disintegrate after a 

 time. After fertilization the egg proceeds to 

 form the embryo of the new plant 



