Influence of Certain Carbohydrates on Green Plants 27 



ment were the same as in the preceding, except that the cultures were 

 kept in the dark in an incubator at a temperature of 32° C. In this 

 experiment the number of plants again differed in the various cultures, 

 but it was found that under the condition of growth — namely, darkness ■ — 

 it is practically immaterial whether or not the number of plants is the 

 same in each culture. When the plants are grown in the light, the greater 

 the number of plants the less is the opportunity for their securing carbon 

 dioxide. In darkness, however, the growth is at the expense of the reserve 

 food or sugar supplied, and the available food under the conditions of the 

 experiment is the only limiting factor. 



The results are presented in table 5. It will be noted that glucose, 

 lactose, and maltose are all better than the check. The average height 

 of the plants is least in the check and greatest in the glucose. The differ- 

 ence in the vigor of the different cultures was plainly visible. It is inter- 

 esting to note that here lactose is apparently utilized, while in other 

 experiments, when the plants were grown in the light, this sugar was not 



utilized. 



influence of lactose 



In a preliminary experiment with timothy it was noted that no increase 

 in growth over the check plants was obcained when lactose was supplied 



TABLE 6. Influence of Various Concentrations of Lactose on Growth 



OF Timothy 



(Plants grown in greenhouse. Duration, December 18 to February 18, 1914, sixty-two days) 



Culture solution 



Number 



of 



plants 



Total 



dry 



weight 



(miUi- 

 grams) 



Average 



dry 

 weight 



per plant 

 (miUi- 

 grams) 



Check (no sugar) \ 2 



,3 



Lactose, 0.1 per cent. 

 Lactose, 0.8 per cent. 

 Lactose, 1.0 per cent . 



Lactose, 2.0 per cent . 



Lactose, 2.5 per cent. 



60 

 59 

 64 

 65 

 60 

 65 

 52 

 68 

 57 



79.4 

 63.0 

 84.0 

 69.0 

 73.0 

 85.0 

 66.0 

 76.0 

 74.0 



1.32 

 1.07 

 1.31 

 1.06 

 1.22 

 1.31 

 1.27 

 1.12 

 1.30 



