DEPARTMENT OF BOTANICAL RESEARCH. 79 



It has, in fact, been observed that leaves of Parthenocissus vitacea manu- 

 facture starch when placed on solutions of 1-arabinose. The nutritive 

 value of the pentoses is still uncertain, but there is Uttle doubt that 

 they are drawn into the respiratory stream, and in the higher plants 

 as well as in fungi and bacteria are of considerable nutritive value. 

 The mode of formation of this group of sugars has not yet been 

 definitely established, and it is of greatest importance in considering 

 the problems of sugar synthesis in the chlorophyllous leaf. By using 

 the improved methods of analysis it was not possible to confirm the 

 older observations that pentoses accumulate in germinating seeds and 

 in the older portions of plants. In the cacti also no such phenomenon 

 was found. Young joints 3 cm. in length were found to contain about 

 the same percentage or even more pentose than the parent joints. Nor 

 could there be discovered any cases in which old joints (three and four 

 years old) had accumulated larger quantities of easily hydrolyzable 

 pentoses, aside from that contained in the cellulose, which naturally 

 is higher in the older joints. The accumulation of pentoses seems to be 

 a function of the water-content; with ample water available the pro- 

 portion of pentoses diminishes, while with decreasing water-content 

 these sugars increase. This is especially noticeable in the course of 

 seasonal variation. This is interesting in view of the fact that the 

 mucilaginous material so prevalent in succulent plants is composed 

 largely of pentosans. However, in pure-water solutions at least, these 

 mucilages exert no effect on the evaporation. 



Gas Interchange in Mesemhryanthemuni and other Succulents, by H. M. Richards. 



During the progress of a previous investigation on gas interchange 

 and acidity in cacti, some experiments were made and a number of 

 gas samples were taken from various other succulents in their native 

 habitat near the Coastal Laboratory at Carmel. Analj^'ses of the above 

 gas samples indicated that it would be desirable to investigate the 

 CO2/O2 relations of these plants more thoroughly. While the number 

 of completed experiments is not large enough to draw definite conclu- 

 sions, there is a strong indication in the case of all the forms used — 

 Dudleya, Mesemhryanthemum, and Ahronia — that the carbon-dioxide 

 evolution may be minimal, less indeed than that in cacti. The oxygen 

 absorption, on the other hand, is very considerable. 



The work of the summer of 1917 has been to collect a large number 

 of gas samples from these forms under various conditions of tempera- 

 ture and illumination and coincident!}'' to study the aciditj^ conditions 

 of the juices. While most of the experiments were, of course, carried 

 on in darkness, not a few were made in diffuse light or direct sunlight; 

 for, as has been shown, the CO2/O2 relations of succulents are highly 

 interesting under illumination, especially in connection with the acidity 

 changes which take place under such conditions. For the purpose 



