FIELD CROPS. 429 



injuries to trees, including a brief discussion of tlie electrical resistance in trees, 

 as well as the effects of alternating and direct currents, liglitning, and earth 

 discharges, and suggests methods of preventing injuries to trees from electric 

 wires. 



It is stated that the effects of alternating currents on trees are local, pro- 

 ducing injury only near the point of contact with the wire. In the author's 

 opinion au alternating current does not cause the death of the tree, although it 

 may burn or disfigure it to a considerable extent. Most of the injury by elec- 

 tric currents is said to be from direct currents used in operating electric rail- 

 roads. In all the experiments conducted the injury was found to be due to the 

 effects of heat generated by the current, and the maximum current for each 

 individual plant was found to vary considerably. 



It is said that there is practically little or no leakage from wires during dry 

 weather, but that more or less occurs during wet weather, when a film of water 

 is formed ou the bark and if insulation of the wires is not sufficient. While no 

 authentic cases of killing trees by either the alternating or direct current as 

 usually employed are reported, it is claimed that the reversal of the polarity 

 in electric railway systems has resulted in destroying a number of trees. The 

 natural high resistance offered by trees and plants in general is said to serve as 

 a protection against severe injury from lightning and contact with high tension 

 wires. The least resistance in a tree occurs in the cambium and adjacent tis- 

 sues. There seems to be evidence to support the idea that a direct current of 

 insufficient strength to cause burning may electrolyze the cell contents and later 

 result in the death of the tree. The author claims that earth discharges during 

 thunderstorms are more common than generally supposed and are known to dis- 

 figure and cause the death of trees. 



Department of botanical research, D. T. MacDougal {Carnegie Inst. Wash- 

 iiif/ton Year Book, 12 (1013), pp. J7-S7, pis. 2, fig. 1). — This is a progress report 

 of the investigations carried on by the director and various assistants at the 

 laboratories of the Carnegie Institution situated at Tucson, Ariz., and else- 

 where. The investigations include a study of the Salton Sea, its geological, 

 chemical, and biological aspects; alterations induced by ovarial treatments of 

 plants; evolution of the chrysomelid beetles; root variation in desert plants 

 (E. S. R., 30, p. 827) ; root characters of trees grown in the coastal climate of 

 California; the transpiration behavior of rain-forest plants; the water rela- 

 tions of plants ; autonomic movements of stems of Opuntia ; the transpiration 

 of desert trees; photolytic effect of blue-violet rays and their variations in solar 

 radiation ; acidity, gaseous interchange, and respiration of cacti ; fruit develop- 

 ment in the Cactacea?; and the relationships and distribution of the Cactacese. 



FIELD CROPS. 



Agriculture, ^Y. Somerville {London, Xcio York, and Toronto, [WIS], pp. 

 17/ -f 2.56). — This volume discusses from the British point of view the funda- 

 mental principles underlying the practice of agriculture under the topics of 

 formation, properties, types, and improvement of soils; principles and use of 

 manures; i-otation of crops; and seeds. 



The key to successful farming, J. Kasmeier {Shawnee, Okla., 1913, pp. IJfS, 

 figs. 69). — In this book the author gives his experiences and describes the 

 methods he used, which were based on four essentials, viz, preserving the rain- 

 fall and moisture, fertilization, sub.soiling. and care of the plant roots. The 

 results of these methods applietl to cotton, corn, potatoes, alfalfa, wheat, oats, 

 tomatoes, sweet potatoes, orchards, and forestry are given, with supplemental 

 suggestions. 



