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1894. ] Papers Read Before Section G. A AO 381 
3. Variability under cultivation is due to some elasticity of 
the species and is thus inherent. 
4. The newer the type the more readily it varies. New 
types are polymorphous, old types are monomorphous. The 
most flexible types have not yet passed their zenith, e. g., 
Cucurbitaceez. The varieties of cereals are so much alike that 
expert knowledge is needed to distinguish them. 
5. Why are new types flexible? A certain answer cannot 
be given but the author believes it explicable on the principle 
of divergence of characters rather than by any rejuvenescence 
ol type. 
BAILEY, L. H.: The struggle for existence under cultiva- 
tion.—The struggle for existence under cultivation can be re- 
solved into figures. Seedsmen estimate that one-fourth the seed 
produced is lost because unsown. (But this is less than nature 
wastes among wild plants.) Three-fourths therefore engage in 
the struggle for existence. Only one in thirty or one in twenty 
ofthese come to anything. The rest are thinned out. This is 
a struggle between members of the same species; therefore the 
struggle sets up a divergence within the species. Added to 
this is the selective agency of the weeder. The same laws 
which govern evolution in feral conditions govern evolution 
under cultivation. : 
MILES, MANLY: Limits of biological experiments. —The 
author contended that evolutionary laws cannot be demon- | 
strated by direct experiment because of the great number of 
uncontrollable factors, a point well illustrated by the many 
valueless feeding experiments. 
