NATURAL FERTILISATION. 139 



charges, when ripe, a cloud of innumerable pollen-grains ; so 

 that the number of these grains in any single catkin must 

 be prodigious. The female flowers are found on the same 

 branches as the catkins, and are also in clusters of from two to 

 six or eight (the future nuts), and are of equally simple struc- 

 ture with the male flowers, being formed of a single pistil en- 

 closed in bracts, the ovary surmounted by from three to five 

 stigmas, the bright crimson threads by \vhich these female 

 flowers are recognised. If one of these crimson threads is placed 

 under an ordinary pocket-lens, it will generally be found to 

 have on its surface several apparently minute particles of dust, 

 which, on further examination, are found to be pollen-grains 

 which have been blown from the male flowers. Each indi- 

 vidual pollen-grain has the power of emitting a " pollen-tube," 

 which perietrates the stigma, reaches the ovary, and by the fertili- 

 sation of the ovule induces the formation of the embryo, and 

 thus the development of the ovule into the fertile nut. Since 

 the only means by which the pollen can be conveyed from the 

 male to the female flower is the agency of the wind, and it is 

 only quite by chance that any of the grains can reach their 

 destination, the reason is obvious of the enormous amount of 

 pollen with which the catkins of the Hazel are furnished. In 

 some plants, the fertilisation of which is effected in the same 

 manner, the quantity of pollen is still greater, and this is 

 especially the case in the Coniferae or Fir tribe. If a Yew-tree 

 is struck with a stick or agitated by the wind at the time 

 when the pollen is being discharged, it will rise in the form of 

 dense smoke, giving the impression of a burning bush ; and 

 American travellers have described how the water of some of 

 their lakes near the shore is covered at certain seasons by a 

 thick stratum of a sulphur-like substance, the pollen blown 

 from the neighbouring Pine -woods. Whether the female 

 flowers of the Hazel are fertilised from the catkins on the 

 same or on a different bush is a point still in dispute. Another 

 instance in which there is little doubt that fertilisation is ac- 

 complished by the wind, though botanists are not quite unani- 

 mous on this point, is that of our common cereal crops, and 

 especially of Wheat. Important in the highest degree from a 

 mere mercantile point of view as is any question connected 

 with the production of our corn crops, it is onlv very recently 

 that any reliable observations have been made on the mode in 

 which the flowers of Wheat are fertilised ; but these have led 

 to some very curious results. When a field of Wheat is in 

 flower that is, in ordinary seasons, in the early part of June 

 each ear will be found to be furnished with a great number of 



