DEPARTMENT OF BOTANICAL RESEARCH. 75 



METHODS OF SUGAR ANALYSIS APPLICABLE TO PLANTS. 



Early in the course of this work it became evident that existing 

 methods of analysis of plant material were open to serious error. It 

 was found that the material must be very quickly dried in order to 

 destroy at once all enzyme actions, which by the usual methods of 

 drying are greatly accelerated for some time by the heat before the 

 material is killed. One per cent hydrochloric acid for hydrolysis proved 

 to be the best; this completely hydrolyzes the polysaccharides, its effect 

 on cellulose is slight, much less than other acids, as sulphuric acid. 

 In making the alcohohc extractions it is exceedingly important that the 

 acids of the plant material be neutralized with calcium carbonate; the 

 addition of alkaUes, as, for instance, ammonium hydroxide (commonly 

 used) , leads to molecular rearrangements. Even under the best of condi- 

 tions it is doubtful whether the various hexoses in a plant can be accu- 

 rately detennined on account of the rearrangement of these sugars. 



A study of the various methods of determining pentoses showed 

 that these are open to several sources of error, and that this group of 

 sugars can be determined with any degree of accuracy only after the 

 removal of all hexose sugars by means of fermentation. 



A special method has been devised for use with the alkaline copper 

 solutions for all reducing sugars. The reduction is carried out, under 

 definite and precise conditions, in a centrifuge tube of special design. 

 This is graduated on the neck and provided with a glass stopper. After 

 the reduction has taken place, the tube is cooled and the solution 

 made up to volume and thoroughly mixed. The tube is then centri- 

 fuged, which results in a compact sedimentation of all cuprous oxide; 

 the supernatant liquid is perfectly clear, and the remaining copper 

 therein can be accurately determined by means of the thiosulphate 

 method. By the employment of this method most of the usual 

 sources of error incident to the use of copper solutions for the deter- 

 mination of sugars are avoided and exceedingly accurate results are 

 obtainable with even very small quantities of sugar. 



SEASONAL VARIATIONS IN THE CARBOHYDRATE CONTENT OF CACTI. 



The vegetation of the desert is exposed to extreme climatic varia- 

 tions. The influence of the various climatic factors on organisms has 

 been extensively studied at the Desert Laboratory from the physical- 

 physiological, ecological, and genetic considerations. Many of the 

 reactions noted in these studies have their origin in the more deep- 

 seated metabolic activities induced by changes in the external condi- 

 tions. In the cacti, as in most vegetable organisms, the nutritional and 

 plastic material is predominantly of carbohydrate nature. The forma- 

 tion of this material, as well as the nature and rate of its metabolic 

 rearrangements and disintegration, are profoundly affected by the 

 climatic complex. The total effects of the various climatic factors 



