FUNDAMENTAL PRINCIPLES 39 



daughter-nucleus becomes gradually retransformed into a 

 resting nucleus, like the one with which we started. 



In reduction (Fig. 31) a new resting nucleus is not 

 organized after the first nuclear division by which the 

 number of chromosomes in each nucleus is reduced by 

 one-half, but this division is followed at once by a second. 

 This is the process of tetrad-division, by which four 

 spores are formed from each spore-mother-cell. The 

 reduced number of chromosomes persists throughout 

 the gametophyte-phase, including the formation of both 

 egg and sperm. When the latter unite, the nucleus of the 

 zygote will, of course, possess the doubled number of 

 chromosomes, which then persists throughout the body of 

 the sporophyte (mature zygote),' until the stage of spore- 

 formation is again reached. These facts are shown dia- 

 grammatically in Fig. 32. 



29. Inheritance. — It is, of course, common knowledge 

 that men do not gather grapes of thorns, nor figs of 

 thistles. A given species of fern always reproduces the 

 same species, and this is true of all plants. It requires 

 only a brief reflection to realize that this must be so, for 

 the beginning of every living thing is always merely a 

 piece of an antecedent organism, the parent. The off- 

 spring would, therefore, naturally partake of the nature of 

 its parent — it is a piece of it — was originally a part of 

 it. Resemblance between ancestor and descendant is 

 commonly regarded as inheritance, but only a little 

 careful thinking will lead us to see that resemblance 

 and inheritance are by no means synonymous. The real 

 nature of inheritance is well illustrated by the inheritance 

 of property by a son from his father. The thing inherited 

 is not an external appearance, but a material substance 



