582 THE AMERICAN NATURALIST. [VOL. XXXIX. 



homologous pairs so that corresponding pangenes or groups of 

 pangenes are brought together and that there may be a mutual 

 interchange or transfer of idioplasm with the result that the 

 chromosomes after separating may contain a mixed set of pan- 

 genes although each is supposed to have a complete assortment. 

 The interchange makes possible all forms of combinations of the 

 pangenes in the two sets, according to the laws of chance, 

 which might be expressed in proportions that would approximate 

 in some cases the ratios of Mendel. If the parents are widely 

 different from one another their idioplasm may not correspond 

 sufficiently to make possible this union and interchange of 

 pangenes so that the process is suppressed and the hybrid is 

 sterile. 



Allen (:O5, p. 247) points out that the union of two spirems 

 during synapsis with the fusion of two sets of chromomeres, 

 according to his account of the lily, offers a number of possibil- 

 ities with respect to the constitution of idioplasm following the 

 reduction mitosis, (i) There may be such a fusion of elemen- 

 tary units that a single idioplasm is formed different from either 

 parent which would of course be distributed equally to the 

 reproductive cells by the subsequent double longitudinal fission 

 of the single (fusion) spirem. This would be expected to give 

 hybrids of much the same form in every instance and these 

 would remain stable (constant). (2) There may be a greater or 

 less mixing or modification of units but without the actual union 

 and formation of a new idioplasm in the hybrid. Then by the 

 splitting of the single (fusion) spirem there might result a dis- 

 tribution of the mixed idioplasm following ratios or proportions 

 approximating Mendel's law. (3) There may be in part a fusion 

 and in part a mixing of idioplasm which would be expected to 

 result in a .varied combination of parental characters in the off- 

 spring. (4) While the chromosomes may be distributed accord- 

 ing to ratios similar to Mendel's principles their respective 

 characters may be greatly modified by their temporary union 

 during synapsis. (5) Portions of the idioplasm may interact 

 upon one another so that when they are separated by the reduc- 

 tion mitoses their character has become variously modified. (6) 

 Finally, Allen, of course, recognizes the possibility that parental 



