SEASONAL VARIATIONS IN THE CARBOHYDRATE-CONTENT. 53 



The proportional values calculated from the results in table 15 are given 

 in table 16. 



Further light on these phenomena can be gained from a study of tables 

 15 and 16, giving the results of analyses of joints from the same plant dur- 

 ing 1917. These cover the periods beginning with the humid winter, then 

 the arid fore-summer, the arid autumn, and finally again the humid winter. 

 The humid summer is not included, as this period is covered in the pre- 

 ceding series. The water-content increases during January, February, and 

 March, though the rainfall was relatively light for this season. Although 

 the total amount of sugar present increases, the relative amounts of the 

 polysaccharides decrease with increasing water-content. The simpler 

 sugars, hexoses or monosaccharides, show again a corresponding increase 

 with increased water-content, both in actual amount and in proportion to 



TABLE 16. Proportional values of the carbohydrate-content of Opuntia phceacantha 

 on the oasis of the analysis of dry material. 



the other sugar groups. The monosaccharides thus reach their maximum 

 in March at a time when the growth activity of the plant commences. The 

 pentose sugars show a relative decrease with the higher water-content. 

 The period from March 1Y to April 25 was an exceedingly dry one, the 

 water-content has dropped, and although the total sugar-content has in- 

 creased, the proportion of these sugars is very different from what it was at 

 the end of the winter rainy season. The polysaccharides have again 

 increased in every respect, the monosaccharides have decreased very 

 decidedly, and the pentosans have increased markedly. During May the 

 arid fore-summer conditions persist, with increased temperatures, and the 

 condition of the carbohydrates as described for April are accentuated ; very 

 marked is the increase in pentosans. The conditions from June to Sep- 

 tember are a repetition of what has already been described for these seasons. 

 The arid autumn brings again the high polysaccharide and low mono- 

 saccharide content with abundance of pentosans. With the falling tem- 

 peratures and rain of winter, the reverse conditions again set in. (The 

 total pentose sugar and pentosan value for December is not reliable, as it 



