DEPARTMENT OF BOTANICAL RESEARCH. 65 



a day, nor in the course of an experiment lasting 20 days. The optimum 

 temperature for these experiments was found to be 27° C. The number 

 of carbon-dioxide determinations made during a period of 24 hours 

 was increased to 4 and in some cases to 6. An apparatus has been 

 constructed which automatically inserts and withdraws the CO2 absorp- 

 tion tubes from the air-stream at any desired time. Thus greater 

 accuracy is obtained in the analysis of the air passing over the plants, 

 and the amount of personal attention and labor involved in the course 

 of an experiment is considerablj^ reduced. A larger variety of material 

 has also been employed, including a number of bulbous plants and the 

 shoots from the potato, as well as several fungi cultures grown on gela- 

 tine, especially Aspergillus niger. All these plants show the same 

 phenomenon : a higher rate of carbon-dioxide evolution during the day 

 than at night; the difference between day and night is great on days of 

 high solar radiation, while on overcast days this difference is but slight. 

 The progress of the investigations has been somewhat interfered with 

 by the unfavorable weather conditions of the winter and spring, and 

 especially by not being able to procure from abroad some instruments 

 necessary for the study of the electrical conditions of the atmosphere. 



Studies in Photosynthesis, hy H. A. Spoehr. 



In the course of the last three years many experiments have been 

 carried out with a view to reducing carbon dioxide by means of light 

 and of experimentally testing the Baeyer formaldehyde hypothesis. 

 By use of ultra-violet light from a quartz mercury-vapor lamp, solu- 

 tions of carbon dioxide and of potassium bicarbonate were reduced to 

 formic acid. The solutions of alkaline bicarbonates yielded the largest 

 amount of formic acid, which seems to be due to the higher concentra- 

 tion of the HCO3 ion in solutions of these salts. A direct reduction of 

 carbon dioxide or carbonates to formaldehyde was never obtained, even 

 in the presence of nascent hydrogen. A reduction of formic acid to 

 formaldehyde by means of Hght also could never be accomplished. On 

 the other hand, it has been possible to synthesize a sugar-like substance 

 directly from formic acid by means of sunhght or ultra-violet hght. 

 This substance, which was obtained in the form of a sirup, has many of 

 the properties of a sugar, such as the reduction of Fehling's solution 

 and TolUn's solution. Algae develop in solutions thereof in the dark, 

 and can use the substance as an only source of carbon. This substance 

 is undoubtedly a very complex mixture, analogous to formose. The 

 chemical investigations are now in progress. It has been found that 

 not only is this sugar-like mixture synthesized in the light, but light 

 also easily decomposes it, so that the final yield is never large. In the 

 decomposing action, besides formic acid, there is formed a volatile 

 substance giving many of the tests for aldehydes. 



