104 



STAMENS. 



[SECTION 9. 



297. An ordinary polleu-graiu lias two coats ; the outer coat tliickisb, 

 but weak, aud frequently adorned with lines or bands, or studded with 

 points ; the inner coat is extremely thin and delicate, but extensible, and 

 its cavity when fresh contains a thickish protoplasmic Huid, often rendered 

 turbid by an immense number of minute particles that float in it. As the 

 pollen matures this fluid usually dries up, but the protoplasm does not lose 

 its vitality. When the grain is wetted it absorbs water, swells up, aud is 

 apt to burst, discharging the contents. Bui when weak 

 syrup is used it absorbs this slowly, aud the tough in- 

 ner coat will sometimes break througii the outer aud 

 begin a kind of growth, like that which takes place when 

 the pollen is placed upon the stigma. 



298. iSome pollen - grains are, as it 

 were, lobed (as in Fig. 315, 316), or 

 formed of four grains united (as in the 

 Heath family, Pig. 317) : that of Pine 

 (Fig. 318) has a large rounded and empty 

 bladder-like expansion upon each side. 

 This readers such pollen very buoyant, 

 and capable of being trans- 

 ported to a great distance 

 by the wind. 



299. In species of Acacia 

 simple grains lightly cohere 

 into globular pellets. In 

 Mdkweeds and in most 

 Orchids all the poUen of an 



anther-cell is compacted or coherent into one mass, called a Pollen-mass, ot 

 PoLLiNiuM, plural PoLLiNiA. (Fig. 319-322.) 



©J 



319 



ing Primrose, the three lobes as large as the central body; 317, of Kalmia, four 

 grains united, as in mo.st of the Heath family; 318, of Pine, as it were of three 

 grains or cells united ; the lateral enijity and light. 



Fig. 319. Pollen, a pair of poUinia of a Milkweed, Asclepias, attached by stalks 

 to a gland; moderately magnified. 



Fig. 320. Pollinium of an Orcliis (Habenaria), with its stalk attached to a 

 sticky gland; magnified. 321. Some of tlie packets or partial pollinia, of wliieh 

 Fig. 320 is made up, more magnified. 



Fig. 322. One of the yiartial pollinia, torn up at top to show the grains (which 

 are each composed of four), aud highly magnified. 



