74 CARNEGIE INSTITUTION OF WASHINGTON. 



before any conclusions can be drawn as to the immediate source of any- 

 particular sugar. Thus, for example, it is not justifiable to conclude 

 that saccharose is the first sugar formed in photosynthesis, merely on 

 the basis of the analyses of the insolated leaf, without accurate knowl- 

 edge of the other sources and conditions which lead to the accumula- 

 tion of this sugar. Again, the mere fact that the total pentoses gener- 

 ally accumulate in the older portions of a plant is no evidence that these 

 substances are to be regarded as waste products coming from the 

 incomplete respiration of hexose sugars. 



These conditions are further complicated by the inherent physio- 

 logical differences of the various kinds of plants, such as that of plants 

 which produce starch easily having relatively only very Uttle soluble 

 reducing and non-reducing carbohydrates, while plants which form 

 little or no starch accumulate relatively large quantities of these sugars. 

 Also, there is now some indication that not only is the rate of the photo- 

 synthetic process influenced by the accumulation of synthesized 

 material, but the process itself seems to require some available food 

 material. This question, it is hoped, will be one of the first subjected 

 to thorough investigation. 



The variations in the carbohydrate equilibrium unquestionably 

 exert a very profound influence on many of the most important physio- 

 logical activities of the organism. It is not possible, however, to 

 indicate any single factor or substance to which can be ascribed such 

 activities as the formation of new shoots or growth in general, nor is 

 such a state of affairs likely to exist, physiological activity in all prob- 

 ability representing the '^ resultant of forces." The manner in which 

 this great complex of chemical equilibria is regulated under varying 

 external conditions allows some insight to be gained into the dynamic 

 processes of the living organism as yet but dimly visible with the aid 

 of chemical and physical conceptions. 



And finally, the conclusions indicate with some definiteness that 

 the results of the investigations of the more intricate phases of plant 

 metabolism are pregnant with concepts which, when considered in 

 their practical application, are not without value to the culture of 

 plants grown for their various conamercial products. 



The method employed consisted essentially in the analysis of rela- 

 tively large amounts of the cactus material which had grown under 

 normal circumstances or had been subjected to special treatment or 

 controlled conditions. The analyses embrace the rate of carbon- 

 dioxide evolution at 28°, the dry weight, total sugars, total polysac- 

 charides, total hexose sugars, hexose-polysaccharides, disaccharides, 

 monosaccharides, hexoses, total pentose sugars, pentosans, pentoses, 

 cellulose, and ash, as well as a series of micro-chemical tests on starch 

 formation and utilization. From these data the condition of equilib- 

 rium of these various components can be readily calculated. 



