50 
SPERMATOGENESIS OF NORMAL 
thus brought together retain their individuality and reappear 
at each cleavage, at least to the twelve-cell stage. Zoja af¬ 
firms that the paternal chromosome is of smaller size and is 
thus distinguishable from the two maternal chromosomes. 
The above interpretations are offered with the hope that 
they may perhaps lead to some clew concerning the real nature 
of the material basis of heredity. If the conception proves to 
be a true one, then it doubtless affords a key, among other 
problems, to the long-standing one, as to why many plants will 
come true from slips or grafts, but not from seed. The reason 
may be sought in the pseudo-reduction period of the germ-cell. 
Plants such as the apple, for example, which do not come true 
from seed, are practically multi-hybrid. In the germ-cells 
there will be numerous incompatibilities due to the fact that the 
plant has been miscellaneously fertilized for a number of gen¬ 
erations. In propagation by means of slips, the chromosomes 
lie side by side and divide in the ordinary way to construct and 
maintain the new body, so that it is practically a continuation 
of the old one; but when the time comes for maturation of the 
germ-cells, the lack of harmony between the various plasmas 
represented asserts itself, with the result that bivalent chromo¬ 
somes are formed, which divide in such a manner as to segre¬ 
gate different sets of ancestral qualities. The resulting com¬ 
binations in fertilization will give rise to seed many of which 
may possess dissimilar sets of qualities. 
Concerning the other abnormalities met wdth in the sper¬ 
matogenesis of hybrids, about all that can be said is that the 
whole phenomena show lack of vigor in the development of the 
germ-cells, whatever this may mean. The deformed sperma¬ 
tozoa indicate want of sufficient vitality to push the develop¬ 
ment through to completion. The germ-cells start out ap¬ 
parently to perform their functions normally, but later suc¬ 
cumb to the conflicting forces at work within their boundaries. 
In most instances where the species are very distinct, the 
hybrids can be obtained in the first place only, as it were, under 
protest; the breeding season must be at its height and every¬ 
thing in the most favorable condition possible. 
As to why the reproductive organs should be more suscep¬ 
tible to abnormal changes than other regions of the body, we 
