Chromatin as ''Ilcrcditarij Substance'' 355 



actually proved connection between licrcdilary attiihutes 

 and chroniosonies. Morgan's livj)()tlie.sis is, houivir, so in- 

 teresting and seems so likely to he proved j)artly true (tluit 

 is, true to the extent of there heino- sonic sort of connection 

 between the attributes in (juestion and clironiosonies ), that 

 it seems desirable to present tlie most salient ])arts of the 

 theory. 



That the case is, as above indicated, still in the hypotheti- 

 cal stage, seems not to be aj)preciated hy some enthusiasts, 

 though fortunately Morgan is not one of these. In t he 

 preface to the volume The Mechanism of Mcndctinn Ilcndil// 

 Morgan writes: "But it should not pass uiuioticed that 

 even if the chromosome theory is denied, theic is jio result 

 dealt with in the following ])ages that may not be treated 

 independently of the chromosomes; for we have made no 

 assumption concerning heredity that cannot also be madi 

 abstractly without the chromosomes as bearers of the postu- 

 lated hereditary factors." ^^ 



The observations on which ^Morgan's hy])othesis rests be- 

 long to two very different categories, and these categories 

 pertain to parts of the organism anatomically far away 

 from each other, namely, to the union and separation or 

 "segregation" of the hereditary attributes of adult organ- 

 isms that propagate bisexually, and to the union and sep- 

 aration of chromosomes of the germ-cells during maturation 

 and fertilization in these same organisms. As an illustration 

 of the first part of this statement take one of Mendel's own 

 cases, that of the table pea having roundish seeds crossed 

 with a variety having angular and deeply wrinkleil seetN. 

 All the seeds of plants arising innnediately from this cross 

 (the Fj generation) are round. But if now the plants of 

 this Fj lot are pollinated among themselves, thiir immediate 

 progeny (the F., generation) will have both lound and 

 angular seeds in the ])roi)ortion of three round to one angu- 

 lar. In a word, since the F^ plants produce seeds corre- 



