24 MASS. EXPERIMENT STATION BULLETIN 436 



After the experiment had been running 80 dajs, all the plants were topped 

 below the terminal growing point, and half the plants which had been at 95° F. 

 soil temperature were exchanged with plants which had been at 70°. The shift 

 was made in April when the daylight period is longer than in February when the 

 experiments were started. The time lag before frenching symptoms appeared 

 in the plants shifted to the high temperature was shortened, possibly because of 

 better growing conditions. The minimum time before the appearance of the 

 pinhead mottling which preceded the development of frenched leaves was re- 

 duced from 21 to 14 days. The same pattern of frenching symptoms was in 

 evidence. Axil shoots which developed on plants shifted to 95° soil temperature 

 had a carry-over of the normal characters of the 70° soil temperature, but even- 

 tually leaves developed with the frenching characters. Plants which had been 

 shifted from 95° to 70° soil temperature also had a carry-over which expressed 

 itself in some cases on the axillary shoots that developed just below the decapi- 

 tated terminal. These shoots showed intense frenching on the lower leaf, but 

 each succeeding leaf was less trenched until an apparently normal leaf was fi- 

 nally produced. There were instances where young leaves, decidedly frenched, 

 began to grow again when shifted to the lower temperature and became wider 

 with less waved margins, but they never developed into leaves of normal shape. 

 On the other hand, no leaves of normal shape developed frenching symptoms 

 when shifted from the low to the high soil temperature. 



These results suggest that soil temperature may play a regulatory role in the 

 frenching of tobacco by affecting absorption or translocation of nutrient elements 

 and may even affect metabolic activity to the extent of creating growth-con- 

 trolling substances either by synthesis or as by-products of a breakdown of 

 chemical compounds within the plant. 



Toxic Effect of Wood Preservatives on Plants. (L. H. Jones.) In previous 

 work with lumber impregnated with asphalt, injury to seedling plants was traced 

 to a small quantity of creosote which had not been removed from the resins. 

 It has now been demonstrated that when the creosote is entirely removed there 

 is no injury to plants from such treated wood. 



It is generally understood that the greatest damage done to green leaves by 

 creosote fumes is by the toxic action of the gas entering the leaf through the 

 stomata. It now appears that damage may be caused also by the dissolution of 

 the leaf, which exposes the tender cells to the dehydrating effect of dry air. 

 Further investigation will be necessary to confirm this type of injury. 



DEPARTMENT OF CHEMISTRY 

 Walter S. Ritchie in Charge 



Factors Affecting the Vitamin Content of Milk and Milk Products. (Arthur 

 D. Holmes.) The investigations that have been conducted under this project 

 during the past year, involve consideration of several factors, but the published 

 papers dealt with two topics: the food value of ice cream as a source of common 

 vitamins, and the vitamin content of mare's milk. 



Ice Cream As a Source of Riboflavin, Carotene, and Ascorbic Acid. (Arthur D. 

 Holmes, John W. Kuzmeski, Carleton P. Jones, and Frank T. Canavan.) Coffee, 

 maple, and vanilla ice creams were manufactured on the commercial scale in the 

 Dairy Laboratory from 24.4 pounds of cream (40 percent), 56.3 pounds of whole 

 milk, 15.0 pounds of cane sugar, 4.0 pounds of skimmed milk powder, and 0.3 

 pound of gelatin. The overrun was 85 percent; i.e., 9.25 pounds per gallon of 

 the ice cream mixture weighed 5 pounds per gallon when frozen. Ten samples 



