728 Journal op the Department op Agriculture. 



FACTORS THAT AFFECT THE GROWTH, REPRO- 

 DUCTION, AND MATURITY OF TOBACCO. 



]^y W. TI. S(iiKKFFirs, M.S., Chief, Division of Tobacco and 



Cotton. 



The various factors that affect the development of a crop of tobacco 

 are numerous. Probably tlie most important are light, temperature, 

 luoisture, chemical changes, and fertility of soil. 



LIgJit. — I have purposely mentioned light first, as too frequently 

 we attach more importance to the other factors mentioned and leave 

 light out of consideration. A number of investigators have given 

 especial attention to this phase of plant life, and their results have 

 indicated that light plays a most important part in the growth and 

 reproduction of plants. This topic miglit be viewed from three 

 directions, namely: (1) Intensity of the light; (2) the quality, that 

 is, the wave lengths of the radiation; and (8) the duration. 



As regards intensity of the light, there seems to be an optimum 

 amount suited for each plant species, and that optimum may be more 

 or less than the full intensity of the sun's light on a clear day in a 

 particular quarter of the globe. AVithin certain limits a reduction of 

 the intensity of the light has a tendency to lengthen the axis and 

 branches and also to increase the superficial area of leaf surface of a 

 good many species of plants. 



1'he effects produced by different spectrum rays are very marked, 

 i hough nothing very decisive can be stated at present, tinder the 

 influence of red rays of light certain species of plants show an 

 abnoimal elongation of the axis, while under green and blue rays the 

 length of the axis is markedly reduced. Some plants show the greatest 

 groAvth under white light. 



The dui'ation of daily exposure to light seems to have an important 

 bearing on the period of veg^etative grow^th of certain species, the 

 lengthening of the daylight period, showing a considerable shortening 

 of the period of vegetative growth, larger seeds pioduced, and an 

 increase in the flavour and aroma. The exclusion of light prevents the 

 development and functioning of the seed-forming agents, or sexual 

 reprodiiction ; on the other hand, the length of the seasonal daylight, 

 or if supplemented by artificial light, is a dominant factor m develop- 

 ing the staminate and pistillate reproductive organs, and, therefore, 

 the existence of the species. 



Only moderate shortening or lengthening of the daylight period 

 tends to retard or accelerate, as the case may be, the sexual reproduc- 

 tion. If the daylight period is too short for production of seed the 

 plant tends to gigantism or indefinite vegetative development. While 

 under the influence of the correct length of daylight for a jiarticular 

 species an abundant flowering and fruiting may be expected. Thus 

 certain varieties may act as late or early niafuiiiig. depending on the 



