418 Tricotylous Races. 
difficult to raise one if it is not. Isolation can be effected 
in two to three generations as a rule, in fact as soon 
as the hereditary values of the plants raised from the 
original mixture of seed have been determined. Very 
little care and no artificial fertilization at all is necessary 
for this purpose. It takes place as quickly in dioecious 
wind-fertilized flowers, such as the hemp, as in self- 
fertilizing species enclosed in bags or cages. 
In the choice of species and varieties one obviously 
has not a free hand. We must first search for cases in 
which the desired races happen to be present, and for this 
purpose sowings of considerable extent have to be made. 
If lots of ten to twenty grams of seed, according to the 
size of the individual grains, are sown, it can be seen 
soon after germination whether the species is likely to 
produce a tricotylous intermediate race or not. The oc- 
currence of 1 to 2 tricotyls amongst about 10,000 normal 
seedlings does not justify this expectation, but that of 
one or more per thousand does as a rule. 
The cultures of my half races mentioned in 4 (p. 
392) had begun in 1892 or earlier, and in the spring 
of 1895 there could be no doubt that I should not obtain 
any intermediate races from them. I resolved therefore 
to seek them elsewhere, and selected for this purpose 
about forty species and varieties of garden plants, which 
were chiefly annuals. The result of this sowing, which 
was conducted on a large scale, has already been given 
on page 380. Most of the sorts contained too few tri- 
cotylous seedlings. Only 8 offered the prospect of giving 
rise to an intermediate race, and of these I had to reject 
three for various reasons. The remaining five, however, 
fulfilled my expectations. 
Before I proceed to the description of my experiments 
