80 CARNEGIE INSTITUTION OF WASHINGTON. 



of exposure to sunlight, use was made of the heat-absorbing glass 

 recently developed by D. T, MacDougal. Flasks exposed under a 

 screen of this glass never rose above 31° C. with the highest insolation 

 encountered at Carmel, while the temperature within naked flasks 

 rose as high as 45° C. 



Over 200 samples have been collected this summer by the method 

 described in a previous publication^ and the vials of gas with mercury 

 seal are to be analyzed at later convenience. This method has been 

 shown to be perfectly satisfactory when care is taken to keep the 

 mercury and containers dry. Analyses in 1917 of samples taken in 

 1913 show no variation from the original determinations. Along with 

 the collection of the gas the necessary acidity determinations have 

 been made. 



In addition, a new method of rapid determination of "total acidities" 

 has been devised. For adequate acidity determinations, speed and 

 simplicity are important factors in order to obviate the errors which 

 may arise by the destruction or neutralization of the unstable organic 

 acids due to oxidation or complicated treatment with reagents. It 

 has been found preferable to sacrifice something of sharpness in the 

 end-point of the titrations in order to insure that the acids are, as nearly 

 as possible, in the original condition in which they are in the plants. 

 This new method consists of taking relatively small samples of the 

 tissues to be examined — 5 grams or even less — and triturating them 

 thoroughly with clean, washed sand. With care the pulp becomes 

 finely comminuted, is then washed thoroughly, filtered, and made up 

 to a definite volume, of which an ahquot portion may be titrated. 

 Repeated trials have shown that, with careful manipulation, the amount 

 of acid left behind in the rejected tissue is negligible. With the use of 

 a centrifuge this method, which has the advantage of speed and sim- 

 plicity as well as of thorough extraction, can be carried through very 

 rapidly. Even with ordinary filtration, in most cases the samples may 

 be titrated within 10 minutes from the beginning of the operation. 



The analyses of the gas samples, as well as further experiments with 

 live plants, will be completed in New York in the Botanical Labora- 

 tories of Barnard College. 



Desiccation and Respiration in Succulent Plants, by E. R. Long. 



The results of some earlier work showed that when the large globular 

 Echinocactus is removed from the soil and dried in the open, stored 

 carbohydrate is formed at a rate exceeding its loss, that a large por- 

 tion of the increase takes place in the "soluble non-reducing sugar" 

 fraction (including cane sugar) , and that in long desiccation, in diffuse 

 fight, oxidation of the stored sugars went on at such a rate that the 

 relative dry weight of the plant- tissue remained constant, as large a 



^Richards, H. M., Acidity and Gas InterchaQge in Cacti, Carnegie Inst. Wash. Pub. No. 209. 



