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Sugarcane is one of the most efficient 1plants for producing carbohydrates by photosynthesis (12); it is therefore of great interest to compare its photosynthetic cycle with that of other plants. Our preliminary experiments (not reported here), in which sections of sugarcane blades were exposed to C1402 for periods up to 15 seconds showed that the radioactivity in 3-phosphoglyceric acid (PGA) was never over 34 % of the total activity incorporated. In no case was this as much as the sum of the activities in malic plus aspartic acids. As a check on our methods of analysis, we exposed a soybean leaf to C1402 for 15 seconds; PGA accounted for 80 % of the total radioactivity.The experiments reported here are part of a continuing study of sucrose synthesis in the sugarcane plant. Materials and MethodsLeaves were selected from 1-year old, field-grown plants of variety H 37-1933. This is a complex interspecific hybrid involving Saccharurn officinarum L., S. spontaneum L., and S. robustum Brandes and Jeswiet ex Grassl (13). Leaf No. 3 or No. 4 (the youngest fully expanded leaves) was cut off, and sections were cut under water from the middle part of the leaf.Tungsten light, filtered through water to reduce heat, gave an illumination of 2000 ft-c at the surface of the leaf. This is well below light saturation for sugarcane (10) and about the same intensity used by many other investigators (1,2,3,4 CO2 was injected to raise the concentration to 0.10 %. Ten minutes later, 500 juc of C1402 were injected. At each scheduled time 1 leaf section was withdrawn and dropped into boiling alcohol; this operation required 1 to 2 seconds.3. The dip method. The procedure was to inject C1402 into a closed glass chamber with a narrow, cellophane-tape-covered slit in the top. The tape was removed, a leaf quickly lowered through the slit, and withdrawn after the selected time.Extractions. Leaf sections were boiled in 95 % ethanol for 5 minutes. Whereas a leaf such as soybean is completely extracted and colorless after this treatment, the sturdier sugarcane leaf appears unchanged although some green color can be seen in the alcohol. Blending with the further addition of alcohol to 50 ml in a Waring blendor resulted in the extraction of most of the sugars and chlorophyll.After filtration, the alcohol-insoluble material was twice boiled for 3 minutes with 20 ml of water and filtered. The residue was again washed with alcohol to facilitate drying. Aliquots of each solution were counted on planchets at infinite thinness. The resiwww.plantphysiol.org on May 11, 2018 -Published by Downloaded from

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