204 K. S. LASHLEY 



There remain only Johannsen's data on Phaseolus giving 

 evidence of an ancestral correlation within the pure line. The 

 evidence adduced by Pearson indicates only a slight correlation 

 here and the recent work of Harris ('12) upon the transmission 

 of the effects of unfavorable cultural conditions indicates that 

 the real cause of this correlation is likewise environmental. 



VI. SUMMARY 



1 . Populations of Hydra consist of hereditarily distinct strains 

 which differ in initial number of tentacles, size of body, color, 

 age at which asexual reproduction is begun, and perhaps in other 

 characters. 



2. In the absence of selection these strains remain distinct. 



3. Within populations there is a correlation between the 

 characteristics of parents and progeny and of other close relatives, 

 which is largely due to the existence of these diverse strains. 



4. Within the clone there is no significant correlation between 

 the variations of close relatives in the initial number of tentacles. 



5. Within the clone there is a slight correlation between the 

 number of tentacles of the buds and the number of tentacles 

 which their parents bear when each bud is produced. 



6. Diversities of environment tend to produce like variations 

 in parents and offspring and this likeness tends to disappear 

 when the environmental cause is removed. The existence of 

 such environmental agents is sufficient to account for the ances- 

 tral correlations found, even though there is no inheritance of 

 variations. 



7. Continued selection of variates in tentacle number results 

 in changes in the vigor of the selected groups. This results in 

 an apparent diversity of the differentially selected groups but 

 the diversity persists only during selection and disappears at 

 once when selection is discontinued. Variations in the number 

 of tentacles of Hydra viridis are not inherited. 



8. There is a positive correlation between the variations 

 in the size of parent and offspring within the clone. No statis- 

 tical evidence of an external cause of this correlation is presented 



