408 De Vries. — On Biastrepsis in its 
nized in comparative experiments with plants : I refer to the 
inequality of external conditions as regards the individual 
seedlings growing on one and the same bed. This inequality 
is much greater than might be supposed, especially during 
germination. It is a familiar fact that the seeds of a sowing 
do not all germinate simultaneously ; and those which ger- 
minate on a sunny day in moist soil are at a great advan- 
tage as compared with those which germinate in dry soil or 
on a dull day. The unevenness of the surface of the soil 
leads to some spots being dry and others relatively moist, 
and germination is so much expedited in the latter that the 
seedlings are often found growing in scattered groups. The 
mixture of the soil with the manure is not uniform, even 
when the greatest care is taken ; and this leads to an unequal 
distribution of moisture in the soil, especially when fresh farm- 
yard manure is used. Then again, injury by birds or insects 
gives rise to great differences among the seedlings. All these 
various conditions have as their result that the young plants, 
after germination is over, soon show striking differences in 
development. According to the goodness or badness of the 
weather in the course of the summer, these differences either 
become more marked or they tend to disappear. And then, 
if the plants are crowded so as to touch each other, the 
existing differences become accentuated, the more vigorous 
developing rapidly at the expense of the weaker. 
Much more in the same strain might be added : but what 
has been said suffices to prove that the individual differences 
between plants growing on the same bed are mainly caused 
by the inequality of the conditions under which they have 
been developed. If now the most vigorous and best-developed 
individuals be selected as seed-bearers, it is almost certain 
that they are those which have been the most highly 
nourished throughout their lives. Selection in this case 
means the selection of the best- nourished. 
It would appear to be quite permissible to extend this 
conclusion to the case of biastrepsis. During the ripening 
of the seeds, during their germination, and then during their 
