9 



find that, speaking generally, those plants whose seeds are 

 scattered by the wind produce a greater number of seeds 

 than those distributed by other agencies. An example of 

 this is furnished by a comparison of the number of seeds 

 produced by two trees which are to be seen side by side in 

 blossom at the present moment. 



I refer to the elm and the nut. Both depend on the 

 wind for their fertilization, the elm depends on the same 

 element for the dispersal of its seeds, the nut on other 

 agencies ; accordingly we find that the elm produces many 

 thousands of seeds, where the nut produces perhaps as many 

 units. 



Where wind distribution is the plan adopted it is to the 

 advantage of the species that the seed should travel a long 

 distance rather than a short one, accordingly we find all 

 sorts of devices for keeping the traveller afloat. Great num- 

 bers of seeds belonging to this class are provided with wings 

 to assist their flight, as in the elm, sycamore, lime, pine, 

 hop, &c. ; others, and these commonly among the compositae, 

 have pappi attached as in the thistle, dandelion, &c. 



Many others have the seed attached to a sort of hairy 

 tail, as in the anemone, clematis, willow herb, &c. 



While speaking of agencies external to the plant itself, 

 I must not omit to mention the part played by birds and 

 animals. The cases are numerous in which seeds in the 

 form of various fruits are taken by birds and animals for food, 

 and either dropped without being eaten, or voided without 

 being digested. In the case of these fruity seeds which are 

 specially taken for food, there is a mechanical limit to the 

 number of seeds that an individual plant can produce, inas- 

 much as the weight of the food substance must be taken 

 into account. It is no uncommon sight to see plants of the 

 food-bearing class weighed down with the wealth of their 

 crop. Any overburdening would injure the individual plant 

 by the destruction of its branches. 



The distance that fruits may be carried by birds or 

 animals is indefinite, and I accordingly treat this as an ex- 

 ception to the rule, as to the number of seeds being greater 

 where the area of dispersal is greater, the number being 

 limited by other considerations. 



