POLLEN: LTS DEVELOPMENT AND USE. 



34i 



the stigma. The fovilla, or the mucilaginous fluid filling the 

 grain, proceeds by endosmose into the tube, and thence to the 

 ovule. An effort has been made to disprove the statement that 

 pollen tubes penetrate the style, and so fertilize the ovules ; but 

 the great mass of evidence, and the statements of many observ- 

 ers who have seen the tubes in contact with the ovules, indi- 

 cate that the tubes sent out from the pollen grains do penetrate 

 the style, and then are brought into contact with and fertilize the 

 ovules. 



It is a strange fact that pollen grains are often entirely inoper- 

 ative on the stigmas of the flowers that produce them. It has 

 been found by many experiments that, when certain flowers are 

 inclosed in nets, and insects thus excluded from them, if the pol- 

 len be applied to the stigma of the flower that produces it, the 

 capsules never set seed ; but, if the pollen of another flower be 

 applied, then the stigma is fertilized and 

 seed is produced. In the California poppy 

 (EschscJioltzia) there is a remarkable in- 

 stance of this. Fritz Muller, in Brazil, 

 found it completely sterile with its own 

 pollen. Darwin, in England, found that 

 even with the Brazilian stock of Muller 

 he could get only a few seeds. Thus the 

 sterility appears to depend on other things 

 besides the pollen, the climate, perhaps, 

 having some effect. Sometimes, too, it 

 happens that, if the home pollen grows, and 

 then foreign pollen be applied, this last 

 grows faster and crowds out the first sort. 



The immense number of pollen grains 

 produced by a single flower apparently mili- 

 tates against the saying that Nature allows 

 nothing to be formed but what is needful. 

 It seems, indeed, a vast waste of material 

 to have such a multitude of grains when 

 so very few would answer the same purpose. In a single flower 

 of the peony there are about three and a half million grains ; 

 a flower of the dandelion is estimated to produce nearly two hun- 

 dred and fifty thousand ; the number of ovules in a flower of the 

 Chinese wistaria has been counted and the number of pollen 

 grains estimated, and it is found that for each ovule there are 

 seven thousand grains. While few fall below the thousands, 

 many rise far above the peony in point of numbers. These are 

 the wind-fertilized flowers, and here Nature must provide for an 

 immense loss of material. Darwin says that " bucketfuls of pol- 

 len have been swept off the decks of vessels near the North Ameri- 



Fio. 8. Pollen on Stigma op 

 Antirrhinum mojus. (After 

 Brongniart.) 



