178 MENDELISM 



stituent units of the plant body. The cells which, 

 together with their nuclei, take part in the process of 

 fertilization are known as gametes, or germ-cells male 

 and female respectively, the latter being the ovum. 



It is less generally known that the endosperm of a 

 grain of Indian corn arises by a very similar process 

 to the one which gives rise to the embryo itself. A 

 second nucleus derived from the same pollen grain 

 fuses with a nucleus situated near the ovum, and to 

 the product of this fusion the endosperm owes its 

 origin. It is further found, so far at least as those 

 characters are concerned to which we shall at present 

 confine our attention, that these two important nuclei 

 hidden in the same female flower are exactly alike in 

 hereditary constitution, and so are the two generative 

 nuclei derived from a single pollen grain. In conse- 

 quence of this fact, the observed character of the endo- 

 sperm may be regarded as a true guide to the nature 

 of the plant into which the associated embryo will 

 afterwards develop. The hereditary qualities of the 

 two are exactly the same. 



It is not difficult to find a variety of Indian corn in 

 which the endosperm is yellow, and another in which 

 the colour of this tissue is white, owing to the absence 

 of any visible yellow pigment. If a female flower of a 

 white variety is fertilized with pollen taken from a 

 yellow variety, the resulting grain shows its hybrid 

 nature by the presence of the yellow colour in its endo- 

 sperm. This is found to be a regular rule. Grains 

 upon a plant of a white strain which has been pollinated 

 with ' white pollen ' are white, but if pollinated from 



