K. Newton 7 



Wheatstoiie bridoe, using a Freas conductivity cell, and finally the 

 hydrogen-ion concentration was determined by means of standard Leeds 

 and Northrup potentiometric equipment. Both of the latter determina- 

 tions were carried out at 25° C. in a constant temperature room. Usually 

 the work on any particular sample was completed within an hour of 

 expressing the juice. 



PreparuUon of Samples for Analysis. As the samples for analysis 

 were collected in the field they were placed directly in tared one-litre 

 erlenmeyers with rubber stoppers. They were frozen when collected, and 

 kept in that condition overnight. Immediately after thawing in the 

 laboratory next day, samples for the determination of dry matter were 

 weighed out; then in addition, sufficient material was removed to leave 

 exactly 100 grams in each fiask. To tills was added 1-5 grams of pure 

 precipitated calcium carbonate for the neutrahsation of plant acids, and 

 sufficient 95 per cent, alcohol to make the final concentration 80 per cent, 

 after allowing for the dilution due to water in the leaves. The samples 

 were then boiled half an hour under reflux condensers, and put away 

 tightly stoppered until a convenient time for analysis. The procedure 

 from thawing to boiling was carried out with the utmost expedition. 



The advantage of using calcium carbonate as noted above has been 

 discussed by Spoehr(}.5). Davis, Daish and Sawyer (9) have pointed out 

 the necessity for rapid destruction of enzymes. In this connection the 

 present study afforded opportunity for sonu^ observations of interest. 

 An additional quantity of one variety was collected for experimentation 

 in methods. Part of this was left five days in an ice chest, and was then 

 put through the regular preparative and analytical procedure. In Table 1 

 the results are compared with those for the same material disposed of 

 promptly after collection. When it is considered that the tissues were 

 not crushed or injured to any appreciable degree, the effect of enzyme 

 action even in such cold storage conditions is very striking. 



Drij Matter. Triphcatc samples of approximately 5 grams of green 

 material were dried to constant weight in a vacuum oven at 98° C. 



Total Nitrogen. The total nitrogen was determined by the Kjeldahl- 

 Gunning- Arnold method, using the residues from the dry matter deter- 

 minations. 



Extraction of Sugars and Soluble Nitrogen. Large extractors of the 

 Soxhlet type were made by drilling a small hole close to the bottom of 

 a 750 c.c. wide-mouthed bottle, and fitting in a glass siphon tightly by 

 making a ground glass joint or by wedging it with a collar of rubber 

 tubing. The bottle was closed with a large rubber stopper, in which were 



