SEED-SCATTERING 277 



the air. Strasburger refers to an experiment with the 

 hairy fruit of the artichoke, which was allowed to sink 

 in vacuo and in the air. " Compared with the accelerated 

 fall in a vacuum, the retardation exerted by the resistance 

 of the air (by which the opportunity for dispersal through 

 the agency of the wind is enhanced) is, in the first second, 

 as six to one." 



Another form of the parachute adaptation is seen in the 

 winged fruits of the maple and the ash and the elm, and 

 some other trees. In the case of the maple there is a 

 heavy nutlet at one end ; the other is prolonged like an 

 insect's wing. If we throw the fruit into the air, as every 

 country schoolboy knows well, it sinks slowly down with 

 a beautiful twisting motion at some distance from where 

 we are standing. So, when this fruit is torn from the 

 tree by the wind, the parachute not only acts in a general 

 way like a float, giving the wind time to get a grip of it 

 and whirl it away, but it causes that peculiar gyrating 

 fall that even on a quiet day carries it far beyond the 

 tree's shadow. The importance of this for the seedling 

 is obvious. 



Any structural peculiarity that increases area without 

 increasing weight will aid in wind-dispersal, and it is 

 interesting to notice that the same result is reached in 

 many different ways. The wings may be expansions of 

 the sepals, or of the seed-box, or of the seeds themselves. 

 " In a Bignonia seed, with its widely outspread glossy 

 wings, the centre of gravity is so disposed that the seed 

 floats lightly along through the air in an almost horizontal 

 course, and with a motion like that of a butterfly " 

 (Strasburger's Botany, p. 291). 



In some cases the currents that transport seeds and 

 fruits are in water, not in air, and there may be structural 

 peculiarities that suit this well, such as water-tight tissues 



