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Allen • — N uclear Division in the 
surprising to find such pains taken to ensure an exact adjustment and fusion of 
the two threads, if they are to be completely separated again at a later stage. 
The latter objection might be met, of course, by supposing that the two 
idioplasms, while remaining distinct in the fusion thread, interact without 
an interchange of substance, as suggested in hypothesis (5), already 
discussed. 
As a result of the comparison which I have attempted to trace between 
the results of experiment and those of cytological study, it seems to me 
safe to say that the intimate contact of the parental idioplasms in the 
prophases of the heterotypic division, and the subsequent separation of 
their substance by the longitudinal splitting of the spirem, produce results 
of different nature in different instances. In a few well-authenticated cases 
(instances of constant hybrids) there appears to be a thorough fusion of 
the idioplasms and a subsequent equational splitting ; although it remains 
possible that a more careful analysis of these same cases may show that 
the fusion is not so complete as the facts now seem to indicate. In 
a considerable number of other cases there appear to be certain elements 
of either parental idioplasm which remain distinct, and by the longitudinal 
fission of the thread are redistributed to the germ-cells according to 
Mendel’s law. In none of these cases has it yet been shown that the 
whole idioplasm is divisible into units which are capable of a Mendelian 
redistribution. 
It remains possible, therefore, that in every case there is at least 
a partial fusion of the idioplasms; and that in every case also certain 
portions remain uncombined and are later separated. The questions 
whether there ever occurs a complete fusion, or whether in any case no 
fusion at all occurs, and whether the problem may not be further com- 
plicated by some of the other factors that I have mentioned, must be left 
for future investigation. 
The studies whose results are embodied in the foregoing paper were 
begun at the suggestion of Professor R. A. Harper, and have been carried 
on under his direction and with the constant assistance of his helpful 
criticism. 
Madison, Wisconsin 
August 8, 1904. 
Literature cited. 
Allen, C. E. (’03) : The Early Stages of Spindle-formation in the Pollen Mother-cells of Larix. 
Ann. of Bot, vol. xvii, p. 281. 
(’04) : Chromosome Reduction in Lilium canadense. Bot. Gaz., vol. xxxvii, p. 464. 
Balbiani, E. G. (76) : Sur les phenomenes de la division du noyau cellulaire. Compt. Rend., 
tom. Ixxxiii, p. 831. 
