BEPARTMENT OF BOTANICAL RESEARCH. 



71 



tionship which was previously determined from 200 trees by Dr. Shreve. 

 In the last 15 years the tree had grown in height 1.9 meters, and in 

 the last 5 years 34 cm., indicating that it was rapidly approaching 

 the period when a mature flat -topped crown is formed. 



In the accompanying table are given the ages and diameters of the 

 trunk at intervals of 2 meters from the stump. 



It will be seen from these figures that 

 between the heights of 4 and 8 meters the 

 tree was growing at the rate of 2 meters 

 per year, and between the heights of 8 and 

 14 meters at the rate of 1 meter per year. 

 The diameter growth of the last 5 years, like 

 that in height, has been greatly reduced, 

 while the thickest rings of growth were 

 made in the years which also witnessed the 

 greatest growth in height. 



The trunk of this pine was found to ex- 

 hibit to a marked extent the alternation 

 of thick and thin rings, or ''double rings," 

 which is frequently observed in this and other species of pines and 

 presents a serious obstacle to the accurate determination of age by 

 ring count. During the 40 years in which this tree has been grow- 

 ing there had been 14 years in which a small accessory ring was 

 formed toward the close of the season's growth. The nature of the 

 latest of these accessory rings is established with certainty through 

 dendrograph measurements made by MacDougal It occurred in the 

 fall of 1918, following a three-day rain of 5 inches in mid-September, 

 and has been detected in several trees by use of the increment borer 

 and in a large number of stumps. 



Carbon-Dioxide-Supplying Power of the Air, by Burton E. Livingston. 



It is generally regarded as proved that ordinary land plants receive 

 their carbon from the air in the form of carbon-dioxide. If this be 

 true, as it surely must be, at least in all cases where the transpiration 

 rate is very low, it is at once suggested that the ability of the sur- 

 rounding air to deliver carbon-dioxide to plant foliage may some- 

 times, or generally, limit the rate of carbohydrate photosynthesis 

 during strongly sunlit periods. Students of this process have been 

 led to the idea that the carbon-dioxide-supplying power of the air is 

 always of sufficient magnitude to surpass the maximum photosyn- 

 thetizing power of green leaves, but several studies point to the con- 

 clusion that this is not generally true. It is at least highly probable 

 that many kinds of plants might absorb and fix carbon at a more 

 rapid rate if the carbon-dioxide-supplying power of the air were 

 greater than it is. Before this question can be adequately studied it 



