Chapter YI 



THE CHROMOSOMES AND MENDEL'S 



TWO LAWS 



The discoveries that ]Mendel made with peas have 

 been found to ap2)ly everywhere throughout the 

 plant and animal kingdoms — to flowering plants, to 

 mosses, to insects, snails, Crustacea, fishes, amphi- 

 bians, birds, and mammals (including man). 



There must be something that these widely sepa- 

 rated groups of plants and animals have in com- 

 mon — some simple mechanism perhaps — to give 

 such definite and orderlv series or results. There 

 is, in fact, a mechanism, possessed alike by animals 

 and plants, that fulfils the requirements of ^lendel's 

 principles. 



The Cellular Basis of Hereditij and Development 

 In order to aj^preciate the full force of the evi- 

 dence, a few familiar facts, that became known be- 

 fore the discovery of the mechanism in question, 

 may be briefly reviewed. 



Throughout the greater part of the last century, 

 while students of evolution and of hereditv were 

 engaged in what may be called the more general 

 aspects of the subject, there existed another group 

 of students who were engaged in working out the 

 minute structure of the material basis of the living 



