76 



CARNEGIE INSTITUTION OF WASHINGTON. 



can be interpreted only by means of an analysis of the influence of the 

 individual factors. The data now available are in the form of monthly 

 analyses of joints from the same plant, in each case, and joints of the 

 same age, formed in 1916: 



Seasonal variations in the car'bohydrate equilibrium of Opuntia sp. 

 expressed in percentages of the dry material. 



Dry weight 



Total sugars 



Total polysaccharides . . 



Total hexose sugar 



Disaccharides 



Hexoses 



Total pentoses 



Pentosans 



Pentoses 



Monosaccharides 



Hexoses to hexose poly- 

 saccharides 



Total pentoses to total 

 sugars 



Jan. 11. 



22.20 



19.10 



15.10 



14.95 



1.27 



2.59 



4.73 



4.40 



0.4.3 



3.02 



.248 



.248 



Feb. 16 



22.30 



21.32 



15.80 



14.90 



1.74 



3.56 



6.07 



5.51 



0.55 



4.11 



.357 



.283 



Mar. 17. 



19.50 



28.05 



20.10 



22.16 



0.93 



6.87 



5.55 



4.75 



0.82 



7.69 



.457 



.198 



Apr. 25. 



24.30 



32.40 



29.84 



22.70 



0.41 



1.86 



9.15 



8.68 



0.48 



2.34 



.090 



.283 



May 22. 



25.25 



30.15 



28.38 



17.08 



0.48 



0.28 



12.34 



12.17 



0.16 



0.44 



.018 



.409 



By the beginning of July the new joints, formed in March, have, for 

 all practical purposes, matured— that is, they show but very slight 

 variation from the joints of the same plant one year older. In fact, 

 the new joints become autonomous very early in their development: 

 young shoots 3 cm. long, when cut from the parent joint, develop 

 normally on nutrient solution. Temperature and the water-content 

 of the joints are principal factors influencing the carbohydrate equi- 

 librium. Among other features, noteworthy in the results of seasonal 

 variation, are the conditions of the joints in March, when new joints 

 appear, particularly the very high percentage of monosaccharides. 



EFFECT OF TEMPERATURE ON CARBOHYDRATE EQUILIBRIUM. 



In general an increase in temperature results in an increase in the 

 katabolic and respiratory processes of a plant, which means that the 

 available simple carbohydrates, the monosaccharides, are more rapidly 

 used up. The monosaccharides are replaced by drawing on the stored 

 polysaccharides by means of enzymatic inversion. At the tempera- 

 tures which prevail in the plant in the summer, sometimes as high as 55° 

 (see McGee, J. M., Rept. Dept. Bot. Res. Carnegie Inst. Wash., 1916, 

 p. 73) in the cacti, the total reserve of carbohydrates would be 

 rapidly depleted and the plant would be in a state of exceedingly 

 high respiratory activity. There is, however, some evidence that the 

 rate of monosaccharide and disaccharide replacement is reduced at 

 these higher temperatures, so that, as it were, there exists an auto- 

 matic adjustment which tends to close the valve from the store of 

 polysaccharides, permitting a smaller rate of flow of inversion from 



