48 STRUCTURAL AXD PHYSIOLOGICAL BOTANY. 



222 223 



224 225 



226 227 



lining is protruded in the form of a delicate tube, where the 

 pollen comes in contact with the stigma. 



381. The shape of pollen grains is very variable ; the 

 spherical 231 , the triangular 228 , the polygonal" 22 , the oblong 230 , 

 are common forms. 



382. Its surface is either smooth or studded with little 

 points 231 . 



383. The pollen grains are usually distinct from each other, 

 but in some cases they cohere in definite numbers ; Ex. 

 Acacia 232 : or in irregular masses ; Ex. Orchidacese 23 * : or are 

 enclosed within a bag, which seems to be the lining of the 

 anther (Endothecium) ; Ex. Asclepiadacese 233 23fi . 



384. In cases where the pollen grains cohere in masses, or 

 are enclosed within bags, they are connected with a cartilagi- 

 nous or elastic process, called the caudicle" 3 *, which adheres 

 to a gland 234 belonging to the stigma. 



385. The function of the pollen is to vivify the ovules 

 (396). 



XII. DISK. 



386. Whatever intervenes between the stamens and the 

 pistil receives the general name of disk. 



387. It usually consists of an annular elevation, encom- 

 passing the base of the ovary, when it is sometimes called the 

 cup , Ex. Pseony. 



388. Or it appears in the form of a glandular lining of the 



