72 PLANT-LIFE ON LAND [CH. 



surrounding a nucleus. It is from this cell that the 

 gametes or male cells are derived. 



The gynoecium or pistil occupies the centre of 

 the flower. It consists in a simple case of the parts 

 shown in Fig. 15. The lower enlarged region is 

 the ovary, the wall of which (fw) protects a single 

 straight ovule. The ovary is continued upwards into 

 a narrower region of the style (g\ and is enlarged at 

 the tip into the receptive stigma (n). It is here 

 that the pollen is received, and retained upon the 

 roughened and often sticky surface. The ovule thus 

 enclosed in the cavity of the ovary consists of a 

 short stalk (fu\ bearing the body of the ovule. 

 From the upper limit of the stalk arise two over- 

 lapping integuments (ie, ii), which closely invest the 

 massive nucellus (nu). This is an oval body of tissue 

 enveloping the large embryo-sac (e\ which has 

 complicated contents. The most important of them 

 is the ovum, or egg, which is the largest of three 

 cells forming a group called the egg-apparatus (ei), 

 which is fixed at the uppermost end of the embryo-sac. 

 The ovum is a primordial cell, that is, it has no 

 cell-wall, and consists of cytoplasm with a nucleus. 

 It is the female cell, and it developes no further unless 

 fertilised. 



The sexual cells or gametes are thus produced 

 apart from one another. The problem is to bring 

 them together when neither is motile, and one is 



