454 



HUTCHINSON'S POPULAR BOTANY 



FIG. 558. POL- 

 LEN-GRAINS OF 

 GREAT PANI- 

 CLED SEDGE (Ga- 

 rex paniculata). 



the North American shore ; and Mr. Riley has seen the 

 ground near St. Louis, in Missouri, covered with pollen, as 

 if sprinkled with sulphur : and there was good reason to 

 believe that this had been transported from the pine-forests 

 at least 400 miles to the south. Kerner has seen the snow- 

 fields on the higher Alps similarly dusted ; and Mr. Blackley 

 found numerous pollen-grains, in one instance 1.200, adher- 

 ing to sticky slides, which were sent up to a height of from 

 500 to 1,000 feet by means of a kite, and then uncovered 

 by a special mechanism." A shower of pollen which fell 

 in Inverness-shire in the year 1858 (our authority is Professor 

 Ainsworth Davis) covered the ground to a depth of half an inch. 



Of the three great classes into which the Flowering Plants are divided 

 namely, Monocotyledons, Dicotyledons, and Gymnosperms one class, the 

 last named, is entirely composed of wind-pollinated plants. The Gymno- 

 sperms derive their names from the fact that their ovules are not contained 

 in an ovary they are naked. The ilowers, which are unisexual and without 

 calyx or corolla, would stand but a p >or chance of perfecting their seeds 

 were it not for the kindly offices of the wind. 



The Scots Pine (Pinus sylvestris) offers a good example of the wind- 

 pollinated gymnosperm. Its inflorescences are cones, the male cones, which 

 grow in clusters, being much smaller than the female. In the month of 

 June the anthers open, and discharge their ivinged pollen, which is furnished 

 with microscopic air-bladders (fig. 495), into the grooved backs of the 

 membranous anther-scales, where it lies ready for the breeze to scatter it. 

 Meanwhile the female cones get ready for the "sulphur shower," and being 

 unprovided with any stigma or subsidiary stigmatic appendage, the naked 

 ovules exude a viscid substance which holds fast the pollen that falls in their 

 way, and which, as it dries up, draws the pollen through the micropyle into 

 the interior of the ovule. The fertilized ovules do not arrive at maturity 

 that is, become ripe seeds for two years ; and hence every female cone 

 may be said to have three periods, which correspond with three distinct 



stages in the development of the inflores- 

 cence. In the first period the cone is 

 green and small, and is seated on one of 

 the very young shoots ; in the second 

 period (i.e. at the beginning of the second 

 yearj the cone is larger, but still green, 

 and of course the shoot has become older ; 

 in the third period the cone being now 

 two years older the scales have become 

 brown and wood} 7 , and the seeds are ripe. 



Among the Angiosperms (Dicotyledons 

 and Monocotyledons) the contrivances for 



FIG. 559. POLLEN-GRAIN MAGNIFIED, 



Showing the intine bursting through the 

 extine as the pollen-tube. 



