[Chap. XXXIII SEXUAL REPRODUCTION IN FLOWERING PLANTS 381 



After the embryo from the egg aborts, an embryo develops from cells in 

 the endosperm. This is the embryo that perpetuates the species. 



Ectogony. Pollination and fertilization directly affect the develop- 

 ment of the embryo and of the endosperm because of the union of the 

 sperms with the egg and with the fusion nucleus. They may also affect 

 the abscission of the pistil as well as the chemical composition, the color, 

 and the time of ripening of the fruit. Their influence on the development 

 of structures outside of the embryo and endospeiTn may be referred to 

 as ectogony. 



Considerable study has been made of the effect of pollination and 

 fertilization on the fruit of the date palm. The pollen from staminate 

 flowers of several different varieties of palm was artificially transferred 

 to the pistillate flower of a single species of palm. The development of 

 the fruits varied with the source of the pollen. The fruits varied in size, 

 in shape, and in the time of ripening. Some fruits ripened as much as 

 10 days earlier than others. 



Ectogony is undoubtedly the effect of hormones from the pollen tube 

 and the developing embryo. Experiments have shown that certain 

 ectogonous effects mav be obtained in plants such as tomato, squash, 

 tobacco, and petunia merely by the application of extracts of pollen to 

 the stigma, or to the cut end of a style from which the stigma has been 

 removed. By this means abscission of the pistils may be prevented, and 

 fully formed seedless fruits may develop from them. 



Xenia. The effect of the sperm upon the development of the endo- 

 sperm may be visibly evident. If, for example, pollen from a certain corn 

 plant that had grown from a seed with blue endosperm is transferred 

 to the stigma of another corn plant that had grown from a seed with 

 white endospenn, and if triple fusion follows pollination, the resulting 

 endosperm may be blue. Similar effects may be seen in form, shape, and 

 chemical composition of the endosperm. The immediate effect of the 

 pollen parent on the endosperm of the ovule parent is known as xenia, 

 and will be described further in a later chapter. 



Self- and cross-pollination. The transfer of pollen from anther to 

 stigma of the same flower or of another flower on the same plant may be 

 tenned self-pollination. The transfer of pollen from the anthers on one 

 plant to the stigmas on another plant is ordinarily referred to as cross- 

 pollination. In Chapter XXXVII, however, it will be shown that two 

 plants may be genetically identical, and what appears to be cross- 

 pollination is equivalent to self-pollination. For example, plants that 



