ture, coloration, and odor of their envelopes may also be considered secondary 

 sexual characters. They are certainly related to reproduction, and especially 

 to bringing pollen near the embryo sac. Yet they cannot be considered spe- 

 cifically male or female, since in most flowers both functions are carried on. 



Like some of the display features in animals, floral colors, shapes, odors, 

 nectaries, may be said to "attract". But they attract chiefly insects rather 

 than pollen. On the other hand, the sticky or fuzzy stigma of many flowers 

 is well adapted to catching and holding any pollen that does come by, whether 

 brought by insects or by the wind. 



Another interesting fact about the flowers is their presence only in sporo- 

 phytes — that is, plant generations that bear asexually produced spores. The 

 envelopes of flowers and the other accessory structures are nevertheless re- 

 lated to sexual reproduction, like the secondary sexual characteristics of ani- 

 mals. And we may consider such structures, in both plants and animals, as 

 elaborations of extras, or "luxuries", which are possible only when a species 

 has become so eflicient that it can draw upon a great deal of reserve or surplus 

 food. 



How Do Plants Scatter Their Seed? 



Seeds and the Species' During the winter the trees and shrubs are bare. 

 But millions of other plants perish entirely. Of thousands of species, nothing 

 remains alive except the hard and inert seeds. It is through their seeds that 

 these species will renew themselves when conditions again make growth possible. 



In the Ufe cycle of a seed-bearing plant, the fruit is the organ within which 

 the seed originates and ripens. We may consider the great variety of fruit 

 forms as related to the protection of seed against possible enemies and dangers 

 — including the danger of remaining right at home. Seeds that are enclosed 

 in edible fruits are often distributed by animals that eat the fruit and then 

 discharge from their intestines the uninjured seeds, as in many berries, vibur- 

 num, and cherrv. 



Many fruits open so suddenly, usually by a twisting of the parts of the pod, 

 that they shoot the seeds to a distance of a yard or more, as in squirting 

 cucumber, lupins, and monkshood. 



Most plants depend upon outside agencies to scatter their seeds for them, 

 as they do for the distribution of pollen. Seeds that are very small, or that 

 have expanded winglike surfaces or tufts of hairs, are scattered by the wind, 

 as in milkweed, clematis, thistle, cottonwood, elm, maple, and linden. 



Such fruits or seeds cannot be said to fly, like airplanes or birds — or even to 

 glide, for they are carried without goal by the winds of chance. 



Some fruits have hooks which catch in the fur of passing animals and are 



^See No. 5, p. 415. 

 409 



