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IntroductionSince the appearance of a paper bv JUMELLE (4) on the effect of low temperatures upon "'assimilation,'" there have been a number of publications dealing with this subject. The chief points of interest seem to have been in locating the maximal and minimal temperatures for photosynthesis and respiration and in plotting the course or rates of these processes with respect to variations in temiiperature. JUMELLE placed the plant material, such as spruce branches and lichens, in apparatus where temperature and light could be varied and attempted to measure changes in the composition of the surrounding air. From his results he concluded that spruee and lichens could carry on "assimilation" at temperatures as low as -30°C. and -40°C., respectively, and that "assimilation" continued at a iiunceh lower temperature than did respiration. His results have beeni questionled and his methods adversely criticized by subsequent workers.EWART (1) reported that manv plants, including Piniuns montana, Taxus baccata, Thuja occidenttalis, and Juniiperuts sabina, following three weeks of January weather often as cold as -150 C. were unable to carry on "assimilation" even whemi exposed to a temperature as high as 15°C. until after a lapse of from 2 to 8 hours of time. Furthermore, respiration was found to be active at temperatures too low for "assimilation," and after plants had been exposed to low temperatures and subsequently to warm temperatures respiration became apparent before "assimilation. " MATTHAEI (5, 6) also questioned the work of JUMELLE. She was able to detect "assimilation" in a detached cherry laurel leaf at -60 C., and agreed with EWART that respiration ocecurred at lower temperatures than did ''assimilation. " ZACHAROWA (8) used potted trees of Picea excelsa and Pinus sylvestris which were from 4 to 5 years old. The trees were kept in small glass houses on top of the laboratory roof and were further protected by a mulch of straw and saw dust which was placed arouncd and over the pots. The temperature

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