8 ON FLOWERS AND INSECTS. [LECT. 



But though the pistil is thus surrounded by a row of 

 stamens there are comparatively- few cases in which 

 the pollen of the latter falls directly on the former. 

 On the contrary this transference is in most cases 

 effected in other ways generally by means of the wind, 

 of insects, or, in some cases, of birds. In the former 

 case, however, by far the greater part of the pollen is 

 wasted ; and much more must therefore be produced 

 than in those cases where the transference is effected 

 by insects. 



One advantage, of course, is the great economy of 

 pollen. We have not much information on the subject, 

 but it would seem, from the few observations that have 

 been made, that half a dozen pollen grains are sufficient 

 to fertilize a seed. But in plants in which the pollen is 

 carried by the wind, the chances against any given grain 

 reaching the pistil of another flower are immense. 

 Consequently by far the greater part of the pollen is 

 lost. Every one for instance must have observed the 

 clouds of pollen produced by the Scotch Fir. In such 

 flowers as the Pseony the pollen is carried by insects, 

 and far less therefore is required; yet even here the 

 quantity produced is still large ; it has been estimated 

 that each flower produces between 3,000,000 and 

 4,000,000 grains. The Dandelion is more specialized 

 in this respect, and produces far less pollen ; according 

 to Mr. Hassall about 240,000 grains to each flower; 

 while in Geum urbanum, according to Gsertner, only ten 

 times more pollen is produced than is actually used in 

 fertilization. 



It might, however, be at first supposed that where 

 stamens and pistil coexist in the same flower, the pollen 



