822 EXPERIMENT STATION RECORD. [Vol. 35 



of its cause. It occurs under both anaerobic and aerobic conditions. De- 

 pression of aerobic respiration is shown when measured by either oxygen 

 consumption or carbon dioxid production. Where oxygen is so scant that some 

 carbon dioxid is produced anaerobically, carbon dioxid has no retarding effect 

 on oxidation. A quantitative relation exists between carbon dioxid concentra- 

 tion and the depression of aeroble respiration as in anaerobic carbon dioxid 

 production. It is held that of the two types of respiration demonstrated by 

 Blackraan and others (E. S. R., 26, p. 822), namely, floating respiration and 

 protoplasmic respiration, it is the former only which is depressed by the re- 

 tarding action of carbon dioxid. 



The main conclusion to be drawn from these results as regards the inhibitory 

 action of carbon dioxid upon growth is that a marked reduction of respiration 

 is involved in the mechanism of carbon dioxid narcosis. It is considered that 

 anaerobic and aerobic carbon dioxid production are processes genetically con- 

 nected in normal respiration, and that the rate of the anaerobic process acts 

 as the limiting factor in normal respiration. 



Osmotic pressures in plants.^ — VI, On the composition of the sap in the 

 conducting tracts of trees at different levels and at different seasons of the 

 year, H. H. Dixon and W. R. G. Atkins {Sci. Proc. Roy. Duhlin Soc, n. ser., 

 15 {1916), No. 6, pp. 51-62, fig. Jf).— In a previous publication (E. S. R., 35, 

 p. 26), the authors showed that sap centrifuged from the wood of trees always 

 contained sugars and salts, the former predominating as a rule. In the present 

 paper, an account is given of a study on the composition of the sap at different 

 levels in the same tree and at different seasons of the year upon closely similar 

 trees. Nine trees were used in the experiments, including 4 deciduous trees, 3 

 evergreens, and 2 sub-evergreens. 



It was found that large quantities of sap may be centrifuged from the con- 

 ducting wood of trees, and that the sap varies in color and in electrolyte and 

 nonelectrolyte content. When in a condition of physiological rest during the 

 late autumn and winter, the osmotic pressure of the wood sap of deciduous trees 

 is small and practically constant. During the early spring the sap is enriched 

 by the addition of large quantities of sugars from the storage cells of the wood 

 parenchyma and the medullary rays, and the osmotic pressure rises in a very 

 marked degree from root to summit. During the late spring, the concentration 

 of sugars is still considerable, being roughly half of the earlier value. The elec- 

 trolytes of the sap are, however, present in much greater concentration than in 

 the early spring. 



In Acer macrophyllum, reducing sugars are never found in the wood sap ex- 

 cept in traces, while sucrose is present in quantity. In the other trees examined, 

 both reducing sugars and sucrose were present, the latter predominating as a 

 rule. During the vernal mobilization of reserves, the reducing sugars consist 

 of hexoses and maltose. At other times, the latter is absent. 



In evergreens and sub-evergreens the seasonal changes are not very striking 

 nor are the gradients of osmotic pressures from root to summit so regular as in 

 deciduous trees. The osmotic pressure of the transpiration sap in the root 

 exceeds that in the stem at certain seasons. 



Imbibitional swelling of plants and colloidal mixtures, D. T. MacDougal 

 (Science, n. ser., U {1916), No. 1136, pp. 502-505) .—Attention is called tu the 

 fact that the swelling of gelatin in distilled water, alkali, and acid has been 

 used as a reference phenomenon in interpreting the water relations of plants, 

 especially in growth. During the course of the studies of growth (which is con- 

 sidered to be largely dependent upon absorption and retention of water), disks 

 of the flattened joints of an Opuntia were cut and so arranged as to show varia- 

 tions in swelling. It was found that both young and old tissues take up more 



