116 PHYSIOLOGY [Bot. Absts., Vol. V, 



PROTOPLASM, MOTILITY 



846. Chambers, Robert. Changes in protoplasmic consistency and their relation to cell 

 division. Jour. Gen. Physiol. 2: 49-68. 1919.— See Bot. Absts. 5, Entry 119. 



DIFFUSION, PERMEABILITY 



847. De Vries, O. Verband tusschen het soortelijk gewicht van latex en serum en het 

 rubbergehalt van de latex. [The relation between the specific gravity of latex and serum and 

 the rubber content of latex.] Arch. Rubbercult. Nederlandsch-Indie 3: 183-206. 1919. — See 

 Bot. Absts. 5, Entry 183. 



848. Dixon, H. H., and W. R. G. Atkins. 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. Sci. Proc. Roy. Dublin Soc. 15: 51-62. 1918.— The aim of this paper is the study 

 of sap composition at different levels in the same tree and the examination of similar trees 

 during the various seasons of the year. Three trees of Acer macrophyllum, two each of lle.c 

 aquifolium and Cotoneaster friyida, and one each of Arbutus unedo and Ulmus campestris were 

 employed. — The sap was centrifuged from the fresh conducting wood of the trees. It was 

 found to vary greatly in color and in content of both sugars and salts. During the late autumn 

 and winter while the trees are dormant the osmotic pressure is small and approximately con- 

 stant throughout the wood sap. The upper portions of the stem and the roots have slightly 

 greater pressure than the central portions. In the early spring large quantities of sugars 

 from the storage cells of the wood parenchyma and the medullary rays are added to the sap. 

 This is followed by a marked increase in osmotic pressure from root to crown, the greater in- 

 crease occurring in the upper part of the tree. During late spring the concentration of salts 

 is very much greater than in early spring. At this time the concentration of sugars is still 

 high, being about half the maximum concentration. — In Acer macrophyllum, sucrose is present 

 in quantity. In the root this amounts to 0.6 per cent in October and 1 per cent in February. 

 In the stem at 10 m. level, where the highest concentrations are recorded, 0.5 per cent sucrose 

 is found in October and 5.5 per cent in February. The reducing sugars are not found at all 

 or only in minute traces. In the other trees both reducing sugars and sucrose were found, 

 the latter usually predominating. In the spring the reducing sugars consisted of the hexoses 

 and maltose, at other times the latter is absent. — In the evergreens, Arbutus unedo and Ilex 

 aquifolium, and in the sub-evergreen, Cotoneaster frigida, neither great seasonal changes nor 

 gradients from roots to crown were observed. At certain seasons the roots may have slightly 

 higher concentrations than the stems. — A. E. Waller. 



849. Loeb, Jacques. Electrification of water and osmotic pressure. Jour. Gen. Physiol. 

 2: S7-106. 1919. — Experimenting with the amphoteric electrolytes Al(OH) 3 and gelatin 

 the author finds that water diffuses through collodion membranes into solutions of metal 

 gelatinates or aluminates as if the water were positively charged, and into their acid salts 

 as if it were negatively charged. The turning point for the sign of electrification of water 

 seems to be near, or to coincide with, the isoelectric points, which is a hydrogen ion concen- 

 tration about 2 times 10 -B N for gelatin and about 10~ 7 N for Al(OH) 3 . When diffusing into 

 solutions of metal gelatinates the rate is determined by the charge of the cation, the rate 

 being approximately 2 to 3 times as great into solutions containing the monovalent cations of 

 Li, Na, K, NH 4 as into those of the divalent cations of Ca or Ba at the same concentrations 

 of gelatin and hydrogen ions. When diffusing into acid salts of gelatin, water — apparently 

 negatively charged — diffuses less rapidly into a solution of gelatin sulfate than into a solution 

 of gelatin chloride or nitrate of the same gelatin and hydrogen ion concentrations. "If we 

 define osmotic pressure as that additional pressure upon the solution required to cause as 

 many molecules of water to diffuse from solution to the pure water as diffuses simultane- 

 ously in the opposite direction through the membrane, it follows that the osmotic pressure 

 cannot depend only on the concentration of the solute but must depend also on the electro- 



