CHAPTERS ON EVOLUTION. 



the " embryo," or young plant, is duly formed within the embryo-sac, 

 and thus, even before the seed is planted, development has already 

 proceeded to a certain extent. In the seed of a pea or bean 

 (Fig. 225), for instance, we readily perceive the rudiment of the 

 stem (/), the beginning of the root (r), and likewise the first 

 appendages or " seed leaves (c}" which that stem will develop. 

 The process of fertilisation, thus described in 

 its essential nature, involves in the case of 

 certain plants some curious details, the mere 

 mention of which may stimulate to an inde- 

 pendent research into botanical lore. Thus, 

 often the pollen-tubes may require, from the 

 length of the style of the pistil, to grow to a 

 large relative extent. In the crocus, the 

 pollen-tube requires to grow to a length of 

 three inches before it can reach the ovules 

 FIG. 225. SECTION OF BEAN. j n the ovary. The number of pollen-grains 

 in flowers may be apparently in excess of all 



reasonable proportions a fact to be accounted for on the well- 

 founded idea that the pollen of a flower is not usually limited to 

 that particular flower's wants, but may be destined to serve for the 

 fertilisation of others of the same species. In the great flowered 

 cactus ( Cactus grandiflorus), Morren says there are about 500 anthers, 

 24 stigmas, and 30,000 ovules. Assuming that each anther contains 

 500 pollen-grains, this will give a total of 250,000 grains to each 

 flower ; and the interval or space between the stigma and the ovules 

 of this plant is about 1,150 times the diameter of the pollen-grains. 

 Nature appears exceedingly lavish in her development of pollen. If 

 the Tennysonian aphorism that 



Of fifty seeds 

 She often brings but one to bear, 



be true as it unquestionably is the apparent over-production of 

 pollen-grains is even more remarkable, although we have to take into 

 account the fact just noted, that the development of pollen bears a 

 relation rather to the species and race, than to the individual necessities 

 of the plant. Otherwise, Fritz Mullens estimate, that in a single flower 

 of Maxillaria there are developed 34,000,000 grains of pollen, must 

 present itself as an inexplicable fact of botanical science. Even the 

 wheat-plant produces about 50 Ibs. of pollen to the acre. The 

 pollen of the cone-bearing plants ( Coniferce\ such as the firs, larches, 

 pines, or that of the catkin-bearers (Amenttfera;), is often borne 

 through the air as showers of yellow sulphur-like dust. This dust, 

 falling in regions where the elements of botany are unknown, cause 

 perturbation amongst the unlearned, and result in the penning of 



