582 THE AMERICAN NATURALIST. | (Vor. 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 (:05, 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. (1) 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- 
"pp (4) While the chromosomes may be distributed accord- 
TEN ratios similar to Mendel's principles their respective 
characters may be greatly modified by their temporary union 
during sy napsis. (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 
