FLAX AND TOBACCO 169 



quality of cured leaf is superior to the ordinary varieties. Com- 

 parative yields show that the Mammoth variety yields 20 to 

 25 per cent, more than other varieties when grown on produc- 

 tive soil. As the Mammoth variety has shorter internodes than 

 ordinary varieties the leaves shade one another. This prevents 

 coarse texture and dark colors even on highly productive soil. 

 The ordinary varieties, when grown on rich soils, yield dark- 

 colored and coarse-textured leaves. The value per acre of the 

 Mammoth tobacco is 30 to 40 per cent higher than ordinary 

 varieties (see Fig. 37). 



Garner and Allard (1920) have studied the effect of relative 

 length of day on growth and development of plants, particu- 

 larly with respect to sexual reproduction. By placing a venti- 

 lated, dark chamber in the field the relative number of hours 

 of exposure to sunlight was controlled as desired. They found 

 that: 



" Normally the plant can attain the flowering and fruiting stages 

 only when the length of day falls within certain limits, and, conse- 

 quently, these stages of development ordinarily are reached only during 

 certain seasons of the year. In this particular, some species and vari- 

 eties respond to relatively long days, while others respond to short days, 

 and still others are capable of responding to all lengths of the day which 

 prevail in the latitude of Washington where the tests were made." 



In the absence of a favorable length of day for bringing into 

 expression reproductive processes in certain species, vegetative 

 development may continue and thus lead to the production of 

 such varieties as Stewart Cuban and Maryland Mammoth which 

 under ordinary conditions never reach the flowering stage. 



"Thus, certain varieties or species may act as early or late maturing, 

 depending simply on the length of day to which they happen to be 

 exposed." 



The Stewart Cuban and Maryland Mammoth varieties of 

 tobacco, as well as several other species were used in a deter- 

 mination of the effect of reduced length of day in forcing flower- 

 ing. In discussing the effects of controlling light as a means of 

 forcing flowering in Maryland Mammoth, Garner 1 says; 



"Under a given length of day favorable to flowering, this type can be 

 1 From a letter written September 14, 1920. 



