igig] CURRENT LITERATURE 517 



tumor formation in plants may be wrong because they failed to recognize the 

 polar disposition to callus formation. He thinks the studies on tumor forma- 

 tion in plants will finally throw much light on cancer development. — Wm. 

 Crocker. 



Effect of illuminating gas on plants. — Wehmer" has studied the effect of 

 passing continuous streams of illuminating gas through the soil bearing potted 

 herbaceous as well as 3-7-year-old woody plants. There was a great difference 

 in the amount of injury, according to the stage of development. In the spring 

 the trees were entirely killed in a relatively short time. This is in general the 

 sort of reaction given by the actively growing herbaceous forms at all times. 

 In late summer and early fall the injury is less marked and is shown mainly by 

 leaf fall, while in the dormant period of winter the trees are very resistant. In 

 the cress the embryo in the resting seed and the seedling stage proved very 

 sensitive. Cuttings stood in gas-impregnated water shewed, with few excep- 

 tions (Ilex), seasonal variations in sensitiveness similar to the plants rooted in 

 soils. In spite of this the author thinks that injury to parts above the soil is 

 in part a secondary result of root injury. The injury is due to toxic conditions 

 of the gas and not to mere displacement of oxygen by the gas, as Sorauer has 

 suggested. The toxic constituents increase or decrease with the conditions 

 that lead to an increase or a decrease in the odor-producing materials. A later 

 paper on the toxic constituents is promised. The author seems to have over- 

 looked most of the literature on the effect of illuminating gas on plants. — 

 Wm. Crocker. 



Aeration systems of leaves. — Neger" has earlier spoken of 2 types of leaves 

 on the basis of the nature of their intercellular systems, heterobaric and homo- 

 baric. In a recent article he compares a heterobaric leaf to a house with 

 thousands of rooms lacking communicating doors, and a homobaric leaf to a 

 similar house with communicating doors present and all open. In the first 

 type the intercellular system is divided into many small isolated regions by 

 the smaller veins, with the resulting possibility of different air pressure existing 

 in each; while in the second the whole intercellular system of the leaf is con- 

 nected and therefore the same pressure exists throughout. Most plants with 

 flat leaves have heterobaric leaves, and the size of the individual chambers 

 varies considerably. In various species of Quercus they run from 1/840 to 

 1/1400 sq. cm., and in Syringa vulgaris from 1/8 to i/io sq. cm. In the same 

 species shade leaves have larger chambers than sun leaves. The following trees 

 and shrubs have homobaric leaves: Evonynms japonica, Ilex aqui^olium, 



'"Wehmer, C, Leuchtgaswirkung auf Pflanzen. 4. Die Wirkung des Gases 

 auf das Wurzelsystem von Holz-pflanzen; Ursache der Gaswirkung. Bar. Deutsch. 

 Bot. Gesells. 36:140-144. 1918. 



" Neger, F. W., Die Wegsamkeit der Laubblatter fiir Gaze. Festschrift zum 

 Ernst St.^hl. pp. 152-161. Jena. 1918. 



