EFFECTS OF SELECTION ON" ALKALOIDS IjST BELLADONNA. 



11 



for cross-pollination and to almost exclude the probability of close fertilization in 

 individual flowers. However, the feeding habits of the principal pollinating insects 

 (mostly night and day flying lepidoptera), which visit in turn many open blooms 

 on the same plant, may tend after all to promote self or close pollination on a consider- 

 able proportion of blooms on any given plant. If all the seeds in a single fruit should 

 mature and produce plants with a high alkaloidal content or any other transmissible 



ii 8 °- 



\.70 . 

 \.60- 



%.20\ 



£3(6) 



J(6) 



7W(t>) 



7W(a) 



6W(6) 



6W(a) 



Fig. 7. — Diagram showing the alkaloidal content of the leaves of first-generation belladonna plants from 

 close-pollinated and cross-pollinated selected parents at two stages of growth during the second season, 

 1914. The percentages indicated represent the average of all the individuals from each parent plant: 

 a, Plants from close-pollinated parents; 6, plants from cross-pollinated parents. 



feature of the seed parent, it does not necessarily follow that the pollen of another 

 individual possessing this feature in a lesser degree might not have a reducing effect 

 on the desired characteristic, as the seeds planted may easily be the result of actual 

 close pollination between different blooms of the maternal plant or even of self- 

 fertilization, of an individual bloom. It is but fair to suppose that a majority of the 

 seeds of a given plant may thus be self-pollinated, notwithstanding nature's adapta- 

 tion of the blooms for' crossing, unless it has been made apparent that belladonna 

 blooms are not receptive to their own pollen or to that of 

 flowers on the same plant, but must be fertilized by 

 pollen produced by another individual. This conclusion 

 has not been demonstrated by any controlled experiments 

 that have come to mv knowledge. 



%so. 



^.ao 



\.60 

 §.S0t 



> 3J& 3(b) 7W(b)7Wo)6W($6»'(ct 



SECOND-GENERATION PLANTS FROM CROSS- 

 POLLINATION. 



Up to this point the investigation has dealt 

 entirely with first-generation plants. During 

 the season of 1914 analyses were made of plants 

 which represented the second generation of the 

 original selected individuals. The seed which 

 furnished these plants was secured from the 

 following first-generation plants in the fall of 

 1913: 6w 7 , 6w 10 , 6w u , 7w„ 2,, 2,, 3„ 3 , 3 7 , 34 2 , 

 % \... '■', \ .,, 35 8 . The plants from 6w and 7w were 

 selected as types of high alkaloid-yielding plants, those from 2 as 

 medium, and those from 3 and 34 as low alkaloid-yielding types, '[nil 

 I was planted in the greenhouse at Arlington, Va., in January, 1914, 

 and the plants were transferred to small pots when of suitable size 



Fig. 8.— Diagram showing the 

 average alkaloida 1 content of 

 all the individual belladonna 

 plants from each parent for 

 the second season, 191-1 : 

 a, Plants from close-polli- 

 natod parents; 6, plants from 

 cross-pollinated parents. 



