DISPERSAL OF SEEDS 



chance suitable positions and grow into mature individuals 

 capable in turn of producing seeds, the success of the species 

 is assured. 



It is obvious that it will be advantageous to have the seeds 

 dispersed so that they may grow at some distance and not compete 

 with one another. This also increases the chance of some seeds 

 finding suitable spots to grow in and thus spreading the plant. 

 The competition of plant with plant is partly a direct competition 

 for food, light, etc., but is largely a struggle as to which can 

 reproduce itself most successfully under the conditions of life. 

 We shall therefore be prepared to find that many plants show ar- 

 rangements for the efficient scattering of their seeds, and that the 

 structure of seeds and 

 fruits must be studied 

 in the light of this. 



The seed consists 

 of a seed-coat enclos- 

 ing and protecting an 

 embryo plant which is 

 ready under suitable 

 conditions to continue 

 its growth. To enable 

 growth to start, the 

 seed contains a larger 

 or smaller amount of 

 food material, either 

 stored in the embryo itself or placed beside or around this within 

 the seed-coat. It is an advantage for the young plant to have a 

 considerable amount of food material with it. It gives it a good 

 start, and enables it quickly to become a self-supporting plant. A 

 large store of food material involves, however, a large seed, and 

 brings as a rule difficulties in the seed-dispersal. We have 

 therefore two opposed needs, that of larger seeds which will carry a 

 store of reserve food material and that of easy dispersal. In some 

 plants the one, in others the other need is more fully met, but the 

 existence of both must be borne in mind in studying the adapta- 

 tions for seed-dispersal. 



The seeds are contained in the fruit, which is developed from 



FIG. 18. The Wood Sage. 3, Flower in the first (pollen- 

 shedding) stage ; 2, flower at the beginning of the 

 second (pollen-receiving) stage ; i, flower at the end 

 of the second stage. (From Mailer's Befruchtung der 

 Blumen?) 



