60 
pearance of flowers, means that sexual organs have been formed 
and germ cells (presumably) have been developed for reproduc- 
tive purposes. In other words, it means the potential beginning 
of a new generation of individuals. For, if the egg in the pistil is 
fertilized by a sperm from the pollen grain, an embryo plant 
begins to grow, which when fully developed, forms the essential 
part of the seed. Here, the seed is also surrounded by the ovary 
wall—the whole forming the ‘‘chestnut.”’ * 
This early blooming is a phenomenon that is to be expected in 
hybrids, and is an expression of what geneticists call ‘hybrid 
vigor’’ or heterosis. Hybrid vigor has been known and studied 
from the time of Koelreuter (1765), who makes the following 
interesting and (for the times) rather surprising remark: “I 
would wish that I or another were so fortunate as to obtain a 
hybrid of trees, which, in respect to the utilization of their wood, 
might have a great economic influence. Perhaps such trees 
among other good characteristics might also have these, that, if 
the natural ones required for their full growth, for example, a 
hundred years, they would reach it in half this time. At least I 
do not see why they should behave differently in this respect from 
other hybrid plants.”’ t 
What a vast difference such precocious flowering makes in our 
problem will be clear when one reflects that it means three years 
between generations instead of ten or more. We do not expect 
the future generations to continue as short as this; but, on the 
other hand, we are no longer counting on ten years as the mini- 
mum time for a single generation. A second cross of one of these 
hybrids, made this year, has yielded two nuts, one of the parents 
being again the American chestnut, from pollen received from 
the U. S. government nursery near Washington, D. C. Since 
these hybrids are still small (about 2 feet high at the beginning of 
ve 
* The two large parts (almost halves) of the chestnut, just as in the bean or 
the peanut, are the first leaves of the embryo; the rudimentary stem and root 
are tiny organs located at the base of these fleshy leaves, where all the parts 
come in contact. 
Quoted from Roberts, H. F. ee hybr ieanon ee Mendel. Prince- 
ton, 1929, p.55. See also Koelreuter, J. G. Vorliufige Nachricht von einigen 
das Gesc ee der Pflanzen era ee V ee und Nie BEI 
Dritte Fortsetzung. 1765 
