THE GENOTYPICAL RESPONSE OF THE PLANT 243 
seen in a natural population of A. litorale are probably in most cases 
due to the occurrence in the same habitat of a mixture of distinct biotypes 
each representing a distinct combination of hereditary characteristics. 
It should not be thought, however, that environmental factors may 
not influence the habitus. Modificatory dwarf forms are often de- 
veloped in the upper part of the beach, probably on account of an 
insufficient water supply. Similar plants differing much in size from 
individuals of the 
same biotype 
growing under or- 
dinary field con- 
ditions are inva- 
riably produced 
when allowed to 
develop in sand 
culture. Fig. 14 
shows the habi- 
tus of two indi- 
viduals belonging 
to the same bio- 
type (field no. 
169) of which the 
one to the left 
has developed un- 
der the normal 
conditions of the 
experimental 
fields, while the 
dwarf to the right on 
has been raised _— PRE 
in sand culture. Fig. 16. Atriplex litorale, field no. 168. 
There is also ano- 
ther group of modifications, viz. the modificatory prostrate forms, 
which afford much interest. The prostrate habit of growth, which 
in some biotypes is a hereditary character (as in field no. 160, fig. 18) 
might sometimes, especially in exposed localities, become developed as 
a result of response to environmental factors. I have in a former 
publication tried to show (TurEssoN 1919 a) that exposure to great light 
intensity produces this modificatory prostrateness. Species belonging 
to the genus Atriplex were also mentioned which possessed different 
Hereditas IIF. 17 
