40 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



ANALYTICAL METHODS or PARKIN. 



The procedure adopted by this and all subsequent 

 workers followed in the main the general outlines of that 

 of Brown and Morris. But owing to the fact that starch 

 is absent from snowdrop leaves, the analyses were greatly 

 simplified, as this involves the absence of maltose also. 

 The material used was dried as rapidly as possible. To 

 check this method, similar leaves were frozen in liquid air 

 and analyzed after extraction. The results quoted here 

 show that drying has not resulted in any very appreciable 

 inversion of sucrose, for the proportion of sucrose to hexose 

 is greater in the liquid-air-treated material than in the 

 air-dried. It is, however, to be noted that the small loss 

 in sugars shown by the air-dried sample, falling as it does 

 chiefly on the hexoses, is probably to be explained as due 

 to respiration of the leaves before the destruction of the 

 oxidases, especially as this type of enzyme is stable up to 

 comparatively high temperatures. Parkin (1911) attrib- 

 utes it to a more complete extraction of the fresh pulp. 

 The amounts recorded are the weights of sugar for 100 

 grammes of dry leaf. 



Cold water was used for the extractions, and after ex- 

 tracting four times it was found that only about one- 

 fortieth part of the sugars was left in the tissues. This 

 does not interfere with the comparative nature of the 

 results, but they are not absolute values. It was found 

 that in the extraction about 0*5 gramme of sucrose, per 

 100 grammes of dry leaf, was inverted by the small quantity 

 of invertase which had escaped destruction at the high 

 temperature. This error affects the absolute values, and 

 it may have a small effect upon the relative figures. 



Another point in which Parkin's procedure differed from 

 that of his predecessors was in his omitting to remove 



