THE POLLEN. 



285 



the petiole of a leaf; the anther, to the blade. The connective 

 represents the midrib ; the lobes or cells of the anther represent the 

 two symmetrical halves of the blade ; and the line of dehiscence is 

 normally along the margins of the transformed leaf. What in the 

 leaf would be cells of parenchyma develop as 



531. Pollen. This usually powdery substance consists of grains, 

 of definite size and shape, uniform in the same plant, but often very 

 different in different species or families. The grains are commonly 

 single cells, globular or oval in shape, and of a yellow color. But 

 in Spiderwort they are oblong ; in the Cicliory and Tliistle tribes 

 many-sided (Fig. 485) ; in the Musk-plant spirally grooved (Fig. 

 480) ; in the Mallow family (Fig. 483) and the Squash and Pump- 



kin, beset with bristly projections, &c. The pollen of Pine (Fig. 

 486), as well as that of the Onagraceas (Fig. 487, 489), is not so 

 simple, but appears to consist of three or four blended cells ; that of 

 all true Ericaceae evidently consists of four gi-ains or cells united 



(Fig. 488). The most extraordinary shape is that of Zostera^ or 

 the Eel-grass of salt-water, in which the grains 

 (destitute of the outer coat) consist of long and 

 slender threads, which, as they lie side by side 

 in the anther, resemble a skein of silk. 



532. Pollen-grains are usually formed in fours, 

 by the division of the living contents of mother 

 cells first into two, and these again into two parts, which, acquiring 

 a coat of cellulose, become specialized cells (36). As the pollen 

 completes its growth, the walls of the mother cells are usually oblit- 

 erated. But sometimes the enclosing cells persist, and collect the- 



FIG. 480-489. Forms of pollen : 4B0, from Mimulus moschatus : 481, Sicyos: 482, Echi-- 

 nocystis; 483, Hibiscus: 484, Lily: 485, Ciohory: 486, Pine: 487, Circsea : 488, Kalmia : 

 489, Evening Primrose. 



