April. 1919] 



The Canadian Field-Naturalist 



TEMPERATURE OF SOIL AND AIR. 



In the dry-belt area it is evident that Douglas fir 

 trees are exposed to the sun for a greater number 

 of hours per day, the soil and atmosphere is warmer, 

 the forests are more open, with freer circulation of 

 air, than Douglas fir forests in the coast area. 

 MAXIMUM ROOT-PRESSURE. 



It appears then that in years when Douglas firs 

 are fully exposed to a long succession of hot, cloud- 

 less days in midsummer, and provided with the re- 

 quisite soil conditions (i.e., temperature and available 

 water) the trees gradually accumulate an excess of 

 carbohydrates during the many hours daily ex- 

 posure to sun, the increasing temperature of the soil 

 enables the cells of the roots to maintain or increase 

 their activity during the night, which in dry-belt 

 regions in midsummer is very short, and during 

 which root-pressure is at its maximum. 



DRY ATMOSPHERE. 



When night comes on, the chlorophyll-containing 

 guard-cells have ceased photosynthesis, the guard- 

 cells become isotonic (i.e., of equal concentration) 

 with the surrounding cells, and the stomata close; so 

 that even during warm nights little evaporation can 

 take place from leaves so well protected with cutin. 

 As a result of the increased root-pressure and ces- 

 sation of transpiration the leaves become gorged 

 with water in which the sugar formed by the re- 

 conversion of starch into sugar is dissolved and 

 exuded as drops at the tips of the leaves. The warm 

 dry atmosphere at that time of the year causes the 

 rapid evaporation of the water, leaving the sugar in 

 the form of drops of various sizes as a deposit at the 

 tip. Occasionally two or three such drops come 

 in contact with each other and fuse to form one 

 large drop, frequently they become so large that 

 they fall from the leaf tips onto the leaves or 

 branches below; a succession of these large drops 

 cause the formation of the larger irregular deposits 

 referred to above. 



There is no doubt about the exudation of the 

 sugar from the leaf-tips; deposits may be found in 

 all stages, from mere traces up to large drops, in 

 some cases just dried as they were about to fall. 



With a knowledge of the ecological conditions 

 under which Douglas fir exudes sugar, one can 

 understand why it may be rare or absent in some 

 years; one or two dull, cool, or wet days would 

 suffice to alter one or more of the factors which 

 play a necessary part in promoting its exudation. 

 A dull day would enable the tree to utilize much 



of the excess sugar or store it as starch or other 

 reserve food. A cool day would diminish the activ- 

 ity of the sugar forming cells in the leaves, and by 

 lowering the temperature of the soil would lessen 

 the activity of the roots, thus diminishing the root- 

 pressure and exudation of water, while a wet day 

 and subsequent evaporation from the soil would 

 more effectually lower both the soil and atmospheric 

 temperatures. Other factors would be affected, bui 

 the above summarizes the main points. 

 ANALYSIS OF THE SUGAR. 

 The results of Dr. Shutt's analysis of two sam- 

 ples one supplied in 1914, the other in 1917 in- 

 dicate a high degree of constancy of composition of 

 Douglas fir sugar. 



The preliminary analysis made in 1914 gave the 

 following results: 



Total sugars after hydrolysis 96.25% 



Reducing sugars 23.3 



The analysis of the 1917 sample furnished the 

 following data: 



Total sugars after hydrolysis 91.91 



Reducing sugars 24.86 



Foreign matter, etc., insoluble in water .64 



Moisture 7.00 



Subsequent to the analysis, a contribution* from 

 the Carbohydrate Laboratory of the Bureau of 

 Chemistry, U.S. Department of Agriculture, Wash- 

 ington, D.C. a laboratory especially equipped for 

 the examination of saccharine substances, reports a 

 complete analysis of the same product. 



A summary of their findings is as follows: 

 "The sample of Douglas Fir manna yielded 

 abcul 50% of pure crystalline melezitose, and there 

 IS evidence that the manna contains sucrose and 

 some reducing sugar probably a mixture of glucose 

 with a smaller quantity of fruc"^ose. The percentage 

 composition of the sample of dry manna that we 

 examined was approximately: 



Melezitose 75-83% 



Sucrose 2.9% 



Reducing Sugars 11.5%" 



Melezitose is an extremely rare trisaccharide of 



the formula C H O which on hydrolysis yields 



IS n2 16 ^ J J 



plucose and turanose, the latter is very difficultly 

 hydrclyscd to glucose and fructose but in the con- 

 ventional methods of sugar analysis, the only pro- 

 duct of hydrolysis having direct reducing action is 

 glucose. 



*The Occurrence of Melezitose in a Manna 

 from the Douglas Fir, by C. S. Hudson and S. F. 

 Sherwood fjoiirnfil of the American Chemical 

 Societv, Vol. XL,, No. 9, 1918). 



library' 



