No. 530] PURE LINES IN STUDY OF GENETICS 



8.3 



ness of this method of attempting to learn the important 

 biological facts nnder consideration. 



2. Some of the genotypes show slight bnt constant 

 differences in structure, which I shall not dwell upon 

 here. 4 



.">. They show most varied differences in their physio- 

 logical characters. These physiological differences may 

 go with differences in form and structure, or apparently 

 they may not — so that we find types that differ, so far as 

 detectable, onhj in physiological peculiarities. 



This fact becomes of great practical importance for 

 all physiological investigations, as a few examples from 

 Paramecium will show: 



(a) The races or genotypes differ in the conditions, both 

 external and internal, that induce conjugation. A worker, 

 using a certain strain, works out the conditions inducing 

 conjugation and gives precise directions for accomplish- 

 ing this. His colleague, with another strain, finds this 

 work all wrong, and the controversy on this ancient 

 question continues. One of my strains can be absolutely 

 depended on to conjugate monthly if certain definite con- 

 ditions are furnished; another under the same condi- 

 tions never conjugates; others show intermediate con- 

 ditions. These differences require no biometric methods 

 for their demonstration. 



(b) Again, the genotypes differ in rate of multiplica- 

 tion; under the same conditions some divide once in 

 twelve hours ; others once in twenty-four or more hours ; 

 others have intermediate periods. 



(c) The genotypes differ as to the conditions required 

 for their existence and increase. Several strains, out- 

 wardly alike, living in the same medium, are cultivated 



