212 GOTE TURESSON 
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the following instances, which also serve to bring out the necessity 
of a closer study of the hereditary variation in relation to habitat. 
Massarrt (1902), in his well known paper on the modifications 
of Polygonum amphibium, shows that the plant in question might be 
readily modified into a land form, a water form and a dune form by 
exposing cultures from one and the same individual to the proper 
environmental conditions. He then concludes that the three similar 
forms of this species found in nature are simply modifications of this 
kind brought about by direct hydromorphosis and aeromorphosis. It 
is clear, however, that the experiment does not prove anything of the 
sort. There may exist genotypical differences in the three forms, as 
found in nature, which would play an important part ecologically. 
Extensive work — including cultivations under the same conditions 
of a great number of individuals of the plant, collected in different 
habitats in nature, and preferably supplemented by breeding experi- 
ments — is necessary in order to settle the point. A similar generali- 
zation of facts, to give another example, has been made by SCHMIDT 
(1899). He finds that Lathyrus maritimus from the coasts of the 
Baltic differs in the anatomical structure of its leaves (these being 
dorsiventral) from the L. maritimus found along the North Sea coast 
of Denmark (which has isolateral leaves). Subsequent experiments 
with the former plant showed that watering with solutions of sodium 
chloride induced a leaf structure (viz. isolaterality) typical of the 
North Sea plant. He concludes that it is to be assumed that the 
direct effect of the sodium chloride, which is found in a higher percen- 
tage in the North Sea than in the Baltic, produces the North Sea type. 
It is at once seen that this is a generalization of facts similar to that 
criticised above. It is a generalization of about the same order as 
the statement that any white flowering Primula sinensis has been pro- 
duced by the cultivation of normal, red flowering Primula sinensis at 
30° C. Even if it is true that red flowering P. sinensis becomes white 
when cultivated at 30° C it is equally true that there exist hereditary, 
white P. sinensis forms (Baur, 1914), e. g. white-flowering at a tem- 
perature at which the former plant has red flowers (viz. at 20° C). 
Thus in the absence of critical acquaintance with the different 
forms of a plant species met with in nature, much speculation as to 
the origin of »adaptive» structures is to be found in writings on ecology. 
The following discussion includes a number of notorious adaptive 
forms, and an attempt is made to ascertain whether the existence in 
nature of such forms is the result of an advantageous response on the 
una" 
