309 
Chromosomes in Living Organisms. 
York-Madeira, would lend itself to this purpose. This hybrid 
appears to be the offspring of the spontaneous crossing of 
Vitis aestivalis and V. Labrusca. On the under side of its 
leaves it presents not only the sunk stomata of V. aestivalis 
and the projecting stomata of V. Labrusca , but also every 
possible intermediate form of stoma. From these facts the 
inference might be drawn that the epidermis of the leaf of this 
plant consists of cells which belong to the type of the father, 
or to that of the mother, or to an intermediate type. If this 
be so, the type must be manifested in the individual cells, 
since the two guard-cells of a stoma are developed from 
a single mother-cell. If now this case is to be explained by 
referring it to a difference in the nuclei of these cells, induced 
by hereditarily unequal division, the attempt might appear 
plausible enough : but such an assumption would be directly 
contradicted by those cases in which the hybrid entirely 
resembles either the father or the mother, cases which have 
been observed not only in the genus Vitis, but also in Ruhus 
and Frag aria. For in these latter cases it is an inevitable 
consequence of the theory of hereditarily unequal division, 
that somewhere in the body of the hybrid there must be 
a preponderance in favour of the parent which the hybrid 
does not resemble ; but, as a matter of fact, this does not 
occur. Hence the only possible explanation seems to me to 
be that the interaction of the chromosomes in the nucleus 
gives rise to phenomena of interference : in those hybrids 
which entirely resemble either the father or the mother, it may 
be assumed that the influence of the chromosomes of the 
one parent is completely neutralized by that of the chromo- 
somes of the other; whereas in other hybrids some charac- 
teristics are weakened, whilst others are strengthened, by 
interference. Similarly, just as in hybrids, so the offspring of 
parents of the same species may either combine the characters 
of the parents, or resemble one or the other more strongly. 
Atavistic phenomena clearly prove that the ids whose action 
is neutralized are not absorbed or otherwise destroyed. 
A very instructive case illustrating this point is that of the 
