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THE AMERICAN NATURALIST [Vol.XLVII] 



The rise in the mean of the population of the F 8 genera- 

 tion of Family No. 56 is due partially to the effect of en- 

 vironment, therefore, in that the mother plant was grown 

 under better conditions, but is probably not to any great 

 extent due to the conditions under which the plants them- 

 selves were produced. 



The better environment of the mother plants does not 

 account for all the rise in the means in populations F 8 

 and F 9 , but it accounts for part of it. It will be noticed 

 that all of the populations grown at Forest Hills had 

 higher means than those grown at Bloomfield and New 

 Haven, although the F 6 mother plants were grown at 

 Bloomfield and not at Forest Hills. The greatest shift 

 of the mean, however, comes in the F 8 and F 9 generations, 

 for the mother plants of both of these populations were 

 grown on the more fertile soil. There is a simple ex- 

 planation of these facts, an explanation that is of great 

 economic importance to practical tobacco growers. A 

 part of the rise in mean at Forest Hills was due to set- 

 ting the plants in the field there when they were in an 

 earlier stage of development than those at Bloomfield and 

 New Haven. They were not set earlier in the season (at 

 least, one year they were set early, one year they were set 

 at the average time and the third year they were set late), 

 but they were set as small plants. When small plants 

 (about 4 inches high) are set in the open the root system 

 is equal to the task of supporting the aerial parts and the 

 plants start right in to growing normally. There is no 

 period of passivity. The plants produce leaves spaced 

 with normal internodes and these leaves develop suffi- 

 ciently to have a commercial value. But when the plants 

 reach a height of 8 or 10 inches in the seed pans or seed 

 beds and are then set in the field, the normal metabolism 

 is likely to be upset for a time. The plant takes some 

 time to recover its equilibrium and start a normal growth. 

 During this period basal leaves begin to develop, but the 

 internodes are so close together that they do not obtain 

 their aliquot share of nutriment, hence they grow only to 

 one quarter or one third their normal size and soon wither 



