FRUITS AND COLONISATION BY SEED. 49 



wind the seeds become jerked loose, and are scattered 

 in every direction. But the wind is not essential, for any- 

 thing which bends the stalks over gives, on the rebound, 

 enough throw to send the seeds a long distance. Orchid 

 seeds have occasionally very beautiful thin membranes, 

 but the seeds are generally so minute that the wind can 

 easily blow them to a great distance. The seeds of one 

 species in fact weigh only y-yVuth of a milligramme, about 

 250,000,000 would be required to make a pound 

 weight, so that the proportion of weight to the surface 

 film of air is exceedingly small. 



The effect of these hairs and wings has been tested. 

 Thus the fruits of an Artichoke in one of Dingler's 

 experiments took 7.8 seconds to fall a distance of six feet 

 to the ground, but after the hairs were removed they 

 only took 1.2 seconds to fall the same distance. 

 Bignonia seed fell six feet in 24.6 seconds with their 

 wings and in 4.6 seconds without. The Maple took 

 5.6 seconds with and only 1.2 seconds without its wings. 



The elasticity of the stalk of the inflorescence is, as 

 we have seen, often of great importance. Very fre- 

 quently, owing to the way in which the fruit dries, the 

 carpels become strained, and on being set free suddenly 

 spring out in such a way that a jerk may be given to 

 the seed. The Broom is the classical example, for Bock 

 described the scattering of its seeds in 1546. The two 

 halves of the pod suddenly break apart with an explo- 

 sion, and the seeds are scattered in all directions. 

 Several other Leguminosae act in the same way, notably 

 the Whin, whose seeds are very often jerked three or 

 four feet away from the parent plant. In the Herb-Robert 

 and other Geraniums, the five carpels are arranged in a 

 circle, and their long pointed ends are united into a com- 

 mon stalk in the centre. When ripe each carpel splits 



(B7) D 



