46 PISTILS AND STAMENS 



paper the drawings in Figure 54 and with lines indicate the parts 

 in A from which the different parts shown in B have come. 



In many plants the endosperm does not remain outside of the 

 embryo as it does in Corn and other grains. If one removes the 

 thin rind-like testa from a soaked Bean, all that remains is the 

 large embryo. The endosperm is stored in the embryo and as a 

 result the embryo is much enlarged and fills the space within the 

 testa. Clover, Alfalfa seed, and many other seeds have the endo- 

 sperm stored in the embryo. Study the Clover seed in Figure 55. 

 Notice that there is apparently no endosperm, and that the much 

 enlarged embryo occupies nearly all the space within the testa. 



In some seeds a stored food known as perisperm occurs. 

 Usually as the ovule develops into the seed, the nucellus is de- 

 stroyed and replaced by the developing endosperm, leaving only 

 the integuments from which the seed coat is formed. However, 

 in the formation of a few seeds, some of the nucellus remains, and 

 a portion of its outer region becomes filled with stored food, thus 

 forming the layer of stored food known as perisperm, which sur- 

 rounds the endosperm and embryo. 



Pollination 



Nature of Pollination. Pollination is the transference of 

 pollen to the stigma. After the pollen is on the stigma, it may 

 produce a tube reaching to an ovule and effect fertilization, or 

 it may lie dormant; but in either case the stigma is considered 

 pollinated. Much pollination occurs in nature that does not 

 result in fertilization. Corn pollen, for example, as it is blown 

 about may fall on the stigmas of various other species of plants, 

 but since no fertilization results, the pollination is not effective. 

 Pollen is usually effective only on stigmas of plants similar to 

 the plant which produced the pollen. Thus Apple pollen is 

 effective only on Apple stigmas, Corn pollen only on Corn 

 stigmas, etc. 



Pollinating Agents. The most important pollinating agents 

 are gravity, wind, insects, and man. In some cases, as in Rice, 

 Wheat, and Oats, where the pollen falls from the anthers to the 

 stigma, pollination depends upon gravity. Even in orchards 

 some pollination may be accomplished by pollen falling from the 

 higher branches. In early spring, before there are many insects, 

 many of our trees, such as Willows, Poplars, Oaks, and Pines, 



