104 



STAMEN8. 



[SECTION 9r 



297. An ordinary pollen-grain has two coats ; the outer coat cliickisli, 

 but weak, and 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 fluid, 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. But when weak 



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

 ner coat will sometimes break through the outer and 

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

 the pollen is placed upon the stigma. 



298. Some pollen - grains are, as it 

 were, lobed (as in Jig. 316, 316), or 

 formed of four grains united (as in the 

 Heath family, Fig. 317) : that of Pine 

 (Pig. 318) has a large rounded and empty 

 bladder-like expansion upon each side. 

 This renders 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 

 Milkweeds and in most 

 Orchids all the pollen of an 

 anther-cell is compacted or coherent into one mass, called a Pollen-matt, o? 

 Pollinium, plural Pollinia. (Pig. 319-322.) 



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

 graius united, as in most of the Heath family; 318, of Pine, as it were of three 

 grains or cells united; the lateral empty and light. 



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

 to a gland; moderately magnified. 



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

 sticky gland; magnified. 321. Some of the packets or partial pollinia, of which 

 Fig. 320 is made np, more magnified. 



Fig. 322. One of the partial pollinia, torn np at top to show the grains (whicb 

 are each composed of four), and highly magnified. 



