1909.] Vegetable Assimilation and Respiration. 



47 



Tlie results of four such experiments are given iu the following table. The materials 

 used in two of these were obtained from assimilation experiments with Tropceolum majus, 

 in the other two from translocation expeiiments with lleliantlms tnherosus. 



The areas in the experiments with Troprvolum were measured by the planimeter 

 method. Any error entering into the determination of the area does not, of course, affect 

 the comparison. 



Table XX. — Comparison between results obtained with a drying oven and with a current 



of dry air at 100' C. 



Weights in grammes per square decimetie. 





Area, 

 sq. cm. 



Oven. 



Air current. 





Dry 

 weight. 



Difference. 



Dry 

 weight. 



Difference. 



Trop:eolum majus I 



46-2 

 41 -8 



0 -2063 

 0 -2179 





+ 0-0116 



0 -1978 

 0 -2088 



+ 0 -0110 





40-9 

 44-9 



0 -2303 

 0 -2322 





+ 0 -0019 



0 -2220 

 0 -2241 



+ 0 -0021 



Helianthiis tuberosus 1 /?% " 

 (6) ... 



60 

 60 



0 -4541 

 0-4111 





-0-0430 



0 -4448 

 0 -4008 



-0-0440 



n («) •• 

 (4) ... 



50 

 50 



0 -4400 

 0 -4066 





-0-0334 



0 -4300 

 0 -3960 



-0-0340 



These results show that although after drying in the oven a further 4 per cent, of 

 water may be driven otf when the material is dried in the current of dry aii- at 100° C, 

 yet the difference in the values for the gain of dry weight is small. The greatest 

 difference is D'OOl gramme per .square decimetre, which is less than 0-2 per cent, of the 

 total dry weight. 



Considering the magnitude of the errors from other sources, this is a fair degree of 

 approximation, so that the water-oven method of drying is permissible for rough experi- 

 ments if care is taken to treat in exactly the same way the two portions of material to be 

 compared, and, preferably, to give them their final drying together. It is not to be 

 recommended if a current of dry air or other gas can be used. 



The apparatus described here is not adapted either in form or size for very general 

 use, although it has served the present purposes admirably. When a comparatively 

 large quantity of material from a number of leaves is to be dealt with, a modification 

 of Broocks' two-necked bottle (" Liebig'sche Ente ")* would probably be more suitable, 

 the current of dry air passing in at one opening, and out at the other, over the leaf 

 material cut up into pieces of moderate size. 



Two other points in Broocks' method are worth noting. He used a current of dry 

 coal gas, and a temperature of 115° obtained with a paraffin bath. The high tempera- 

 ture, although unnecessary, probably increases the rapidity of drying, and the gas 

 current could be used with great economy by passing it, carefully dried, over the material 

 on its way to the burner. 



* Loc. cit., p. 16. 



