sessing this unit, will give fertile offspring. The study of the 
heredity of this family of tobacco plants has already covered six 
years, and involves records of over 7000 pedigreed plants. At 
present, some forty strains of tobacco, all related to the original 
monster plant found in Cuba, are growing in the Brooklyn 
Botanic Garden, and some of the individuals of these strains have 
far outdone that ancestor in monstrousness. 
Now, what can one learn from the history of a family of mere 
tobacco plants? What valuable truths are to be deduced from 
such studies? Dare we apply the knowledge derived from a study 
of heredity and environment in tobacco plants to other plants and 
animals, particularly to man? As to the first two questions, one 
may say that such material as peas, beans, wheat, and commer- 
cial tobacco are about the best material one can find for unravel- 
ing the problems of heredity, because these plants ordinarily are 
self-fertilized, and hence freer from character mixtures than 
cross-fertilized plants and bisexually produced animals. All sex- 
ually produced organisms are believed to possess in each of their 
body cells two hereditary units, identical in every way, for each 
character or set of characters in which they breed true. At 
present, we know very little experimentally about the heredity of 
the majority of the character-producing materials of an organism. 
We know even less about the effect of the presence of the various 
kinds of character-forming material upon each other. We have 
very little conception of how many kinds of independent heredity 
units there are in even the simplest plants and animals. We do 
know, however, that some of these character materials cover up 
or obscure the presence of others. In attempting to secure a con- 
ception, then, of how an organism is put together, as to which 
characters are due to the presence of certain units, and which are 
due to the presence of other units, when all the units are under 
the same external environment, we must secure the best material 
possible— material most free from “impurities” or mixtures, ma- 
terial most likely to be pure, or homozygous, for each character. 
Otherwise, confusion indescribable results, and we get nowhere, 
save in accumulating interesting and inexplicable facts. So in 
using such simple material as tobacco or peas for our studies 
on heredity, we succeed in obtaining clues as to how the problems 
of inheritance and environment are to be solved. And what we 
find to be true in simple material, of course, helps us immensely 
in interpreting experimental data from complex material, such as 
man. The solving of difficult problems is, in some respects, 
similar to constructing a fine, durable building, for in both, suit- 
able material to work with is a very essential feature. Any kind 
of material will not do. Mendel foresaw that fact when he began 
his studies on heredity, and it was for that reason mainly that he 
