120 PLANT GROWTH 



Stimulus, not understood, which causes the fruit to grow. If 

 fertiHzation takes place in ovules in only one side of an apple, 

 the unfertilized side will get little stimulus and the apple will 

 be poorly developed. If none of the ovules are fertilized the 

 ovary soon falls from the plant. Recent investigators have 

 been able to stimulate the growth of fruits like tomatoes by 

 applying a chemical stimulator on the stigma. Such fruits 

 are without seeds. 



Xenia is the domination of the sperm over the polar 

 bodies in the development of the endosperm. This is evident 

 in the case of the pollination of sweet corn by field corn. The 

 sperm from field corn dominates and determines the charac- 

 ter of the endosperm causing it to be starchy like field corn 

 instead of sweet like the character of the polar bodies. Sweet 

 corn grown near field corn will have many starchy kernels 

 on an ear, which will be very conspicuous when the corn is 

 ripe because of the sunken sweet corn kernels. If field corn 

 is pollinated by sweet corn pollen the sperm will not dominate 

 field corn polar bodies, therefore the endosperm will be 

 starchy. This also occurs where colored strains are crossed, 

 resulting in ears with kernels colored like the male parent. 



Metaxenia is a term coined by Dr. Swingle a few years 

 ago to describe the influence of the pollen on the fruit. It 

 should be remembered that the tissue of the fruit is from the 

 female parent and therefore bears only genes of that parent, 

 hence any influence of the pollen on the fruit tissue must be 

 carried by a diffusible substance. This influence was first 

 described about two hundred years ago, but has been studied 

 by only a few people. 



A number of crosses have been made with apples; in cer- 

 tain of these, very definite increase in size, sugar content, 

 acidity, and keeping quality resulted from the pollen influ- 

 ence. In any work of this kind it is important to remember 

 that the size of the fruit may depend to some extent on the 

 number of developed seeds. Here again a stimulus passes 



