Live Stock Breeders' Association. 91 



Every cell has in it a nucleus. But the important thing for 

 us to remember here is that those cells which are used for pur- 

 poses of reproduction have only half of a complete nucleus. For 

 this reason the reproductive cells, generally speaking, are incapable 

 of growth until they have united with another reproductive cell, 

 and thus acquired a whole nucleus. 



The reproductive cells, with their half nuclei, are produced 

 by a very different kind of cell division from that which occurs in 

 ordinary growth. Instead of each of the parts of the nucleus 

 dividing, as is the case in ordinary body cells, the parts of the 

 nucleus separate into two groups, so that the reproductive cells 

 which are formed at this division have only half of a nucleus in 

 them. Now it is in this peculiar cell division, which results in the 

 production of reproductive cells, that we find the cause of Mendel's 

 law. Let us now return to our pair of antagonistic characters. 

 Suppose we have a plant which is a hybrid between a red pea 

 and a white one. Every cell in this hybrid plant has both of these 

 characters present in it. But when the reproductive cells are 

 produced, when the nucleus is separated into the half nuclei, we 

 find the red flower character in one of these half nuclei, and the 

 white flower character in the other. Thus half of the newly 

 produced reproductive cells contain the red and half the white 

 flower character. We thus see why we call this law the "law of 

 separation of character pairs," Every pair of antagonistic charac- 

 ter present in a hybrid is thus separated at this particular cell 

 division. 



Let us see now how many and what kinds of seed our hybrid 

 pea produces. Our plant produces reproductive cells in two 

 different places. In the little pod in the center of the flower it 

 produces certain cells called ovules. These contain only half a 

 nucleus, and can not grow and divide in this condition. Half 

 of these ovules contain the red flower tendency, the other half the 

 white. The pollen grains produced in the anthers are likewise 

 reproductive cells. These are also half red and half white ; by this 

 we mean, of course, that half of them contain the red flower 

 character, the other half the white flower character. 



These pollen grains fall on the stigmas at the top of the 

 little seed pod, and grow down into the tissue of the pod until 

 they come in contact with the ovule. Then the half nucleus of 

 the ovule united with a half nucleus from the pollen grain, and we 

 have a new cell with a whole nucleus. This cell then begins to 

 grow, and soon a seed is produced. 



