POLLEN-GKAINS. 81 



If these golden cushions carried on pillars of ivory afford an 

 agreeable spectacle to the naked eye, our admiration increases 

 when we come to view the pollen-grains under a magnifying- 

 glass for every genus of plants has its own characteristic form 

 of this fructifying dust, the surface of which is often most 

 curiously marked. Its roughening by spines or knobby pro- 

 tuberances is a very common feature, and answers the purpose 

 of enabling it to adhere more readily to the stigma. 



These elegant little globes are so small that they generally 

 attain a diameter of only l-l,200th or 1 -3,000th of an inch; 

 while they are so numerous that frequently many thousands are 

 brought forth by one single flower, and thus the seed we tread 

 under foot produces with a boundless prodigality objects so 

 exquisitely formed and modelled that the most skilful pencil 

 can hardly do justice to their beauty. 



Even the pollen-grain which the vernal wind carries in count- 

 less billions through the air, and which man scarce ever deigns 

 to notice, is the work of a consummate master, a wonderful 

 monument of Almighty power ! 



Although both the pistils and the stamina are essential 

 organs of fructification, and seed can only be formed by their 

 mutual co-operation, yet they are not always united in the 

 same blossom. Sometimes, as in the birch, we find flowers of 

 different kinds on the same plant, some bearing pistils and 

 others stamens only ; or, as in the willow and poplar, stamens 

 on one plant and pistils on another ; or, even as in the common 

 ash, the same tree will bear flowers of three different kinds. 



In most plants, however, the pistils and anthers are united 

 within the same corolla, an arrangement which greatly facilitates 

 the admission of the pollen to the stigma; and for the same 

 purpose the stamina of most plants surround the pistilla, an 

 arrangement which gives the pollen an opportunity of falling 

 upon the stigma at every breeze of wind. In those flowers 

 which stand upright, the stamina are higher than the top of the 

 pistil, so that, as the pollen is specifically heavier than air, some 

 of it must almost inevitably fall upon the stigma as soon as it- 

 detaches itself from the anther, while in those flowers which 

 hang down or incline to one side, the pistil is longer than the 

 stamina. 



The flowers of most plants expand by the heat of the sun, 



G 



