CONTROL OF NUMBER OF LEAVES. 33 



in this bulletin, in this way preventing intermixture with undesirable 

 strains by accidental cross-pollination. 



THE CONTROL OF THE NUMBER OF LEAVES ON INDIVIDUAL 



PLANTS. 



The variation in the number of leaves borne by individual plants 

 is just as marked as the variation in size and shape, but the size and 

 shape are not always correlated with the number of leaves. In a gen- 

 eral way it has been the observation of the writers that in cigar- 

 wrapper tobaccos the plants which produce the best-shaped leaves 

 usually produce more than the average number of leaves. The varia- 

 tion in the number of leaves on individual plants grown in the same 

 field may be almost invariably attributed to the lack of systematic 

 seed selection, to crossing, and to the use of a large proportion of 

 light, weak seed in planting. The variation may be correlated with 

 the height of the plants or the length of the internodes, or both. 

 Different strains of the same variety are extremely variable in respect 

 to the number of leaves produced, and until pure strains are devel- 

 oped no very great degree of uniformity in the number of leaves 

 borne by individual plants in the crops may be expected. The pro- 

 duction of strains true to type and uniform in the number of leaves, 

 as well as other characters, is made possible by the careful selection 

 of seed. 



The control of the number of leaves is directly associated with the 

 yield of the crop, and bears a very important relation to success in the 

 handling and curing processes. The possibility of procuring a larger 

 number of desirable leaves on each plant thru careful selection of 

 seed is no longer doubtful, as is clearly borne out by experiments in 

 tobacco breeding. An increase in the production of leaves borne by 

 individual plants has been effected without any increase in the height 

 of the plants and with no detriment to the quality of the tobacco. 

 The reduction in the height of the plants is especially important in 

 Sumatra tobacco grown under shade. It is difficult to prime or pick 

 the top leaves from plants over 7 or 8 feet high, and it would not be 

 advisable for the grower to produce plants which must be topt 

 above that height. The most convenient height for a tobacco shade is 

 about 9 feet. A tent higher than this would be difficult to build, and 

 would be more liable to damage from severe windstorms; hence the 

 necessity for keeping plants below this height by growing more 

 leaves on each plant or by producing plants bearing shorter inter- 

 nodes. The Sumatra and Cuban varieties have a tall habit of 

 growth, with long internodes, but respond readily to methods of 

 breeding in the production of shorter stalks and shorter distances 

 between the leaves. 



15507— No. 90 — 07 m 3 



