How Plants Perpetuate Their Kinds 285 



derived from the male and those derived from the female parent, 

 split lengthwise into two, and one of the halves goes into one new 

 cell and the other into the other; and they absorb nourishment 

 and grow with the cell. This process is then repeated with every 

 subsequent division, so that finally every 

 cell of the adult plant contains chro- 

 mosome material derived from each one 

 of the parents of that plant. This fact 

 helps to explain how it is that a plant or 

 an animal can resemble either one of its 

 parents in any detail of its structure. 



At this point I will pause for a moment 

 to consider two matters of minor impor- 

 tance which may have occurred to the 

 reader. If the fertilized egg-cell contains 

 the sum of the chromosomes of the two 

 uniting nuclei, why is not this number 

 doubled again in the next generation, 

 and that again doubled in the next, and 

 so on to their enormous multiplication? 

 The explanation is simple; at some period 

 in the development of the new sexual 



Cells, by a method Which We need not FIG. 99.-A generalized drawing 



here trace in detail, the number of of a ! im f le ? va |7 and Y ule 



' seen in longitudinal section, 



Chromosomes IS reduced tO One-half. In showing the parts concerned 

 . . . , , ill fertilization. 



the second place, if every cell contains 



within itself chromosome matter derived from both parents, and 

 therefore has the possibility of resembling either one of its parents 

 in any detail of its structure, what is it that determines which one 

 it shall resemble? This we do not yet know, but the probability 

 would seem to be that in each case the stronger of the two elements 

 overpowers the other and reproduces its like. 



The equal contribution of chromosome matter by male and 

 female nuclei, together with the subsequent regular splitting of 



