156 EXPERIMENT STATION RECORD. 



inflates the cells until many of them can not resist the strain, and consequently 

 burst. Atmospheric oxygen, together with the enzyms present, acts on the tan- 

 nin, producing dark-colored oxy-compounds, while further diastatic action is 

 inhibited thereby leaving unaltered many primary starch grains in the vicin- 

 ity of the necrotic tissues. 



It is claimed that excessive transpiration during the day, followed by its 

 sudden checking and complete abeyance during the night, when root action 

 is still vigorous owing to the warmth of the soil, are the main factors in pro- 

 ducing this disease. 



The only remedy suggested is the growing of South African varieties from 

 seed sown there, and thus building up an orchard adapted to its environment. 



On the outbreaks of apple mildew, G. LiJSTNER {Ber. K. Lehranst. Wein, 

 Obst u. Gartenhau Geisenlieim, 1909, pp. 120-123). — A brief discussion is given 

 of the various outbreaks of mildew (Podosphcera leucotricha) in recent years, 

 and its prevalence and severity in 1909 on both apples and pears. 



The destruction of the diseased branches on which the perithecia are found 

 is recommended, and the use of sulphur and lime-sulphur spray is also sug- 

 gested. 



Observations on the dying of Rhenish pear trees, G. Liistner {Ber. K. 

 Lehranst. Wein, Obst u. Gartenbau Geisenlieim, 1909, pp. 123-125). — In experi- 

 ments on the control of this disease it was found that wrapping the trunks of 

 pear trees with straw was of value in preventing it, while whitewashing the 

 trunks proved worthless. 



The author claims that the dying of the trees is probably due to sun scalds 

 and excessive drying of the tissues of the bark, while invading fungi, such as 

 Talsa Icucostotna, play only a subordinate role. The propagation and planting 

 of resistant varieties is recommended as the best means of prevention. 



Contribution to the study of Bordeaux injury on peaches, B. H. A. Groth 

 (New Jersey Stas. Bui. 232, pp. 8-19, pis. 2). — The results are reported of a 

 series of experiments for determining the conditions necessarj' to produce 

 .Bordeaux mixture injury, in which the following questions were investigated: 

 The dependence of the injury on the absolute amount sprayed on the leaves; 

 the comparison of a liniewater spray without the copper sulphate and the usual 

 Bordeaux mixture spray as to injuries produced; the effect of Bordeaux mix- 

 ture on the detached branches; comparison of the injuries to apples, peaches, 

 and plums ; the possibility of Bordeaux mixture injury in a greenhouse sheltered 

 from rain ; differences in the injury caused by Bordeaux mixture of different 

 strengths ; relationship of improperly mixed Bordeaux mixture to leaf burn ; 

 tests for injury on peach trees protected from rain ; the solubility by rain water 

 of the copper in Bordeaux mixture ; atmospheric humidity alone as the deter- 

 mining factor ; the presence of water on the sprayed leaf as a condition favor- 

 able to Bordeaux mixture injury ; and a comparison of the sensitiveness to Bor- 

 deaux mixture of the upper and lower surfaces of peach leaves. 



The following general conclusions were drawn as a result of these experi- 

 ments: (1) Bordeaux mixture injury on peach leaves may occur after a very 

 light spray, an ordinary spray, or a very heavy spray; (2) the copper in the 

 Bordeaux mixture is the injurious factor; (3) peaches are more sensitive to 

 Bordeaux mixture injury than apples; (4) Bordeaux mixture injury to peaches 

 may occur in the laboratory under certain conditions combined, viz, a covering 

 of water on the leaves, a high atmospheric humidity, an excess of respiration 

 over carbon dioxid assimilation, and shade; (5) a peach leaf is attacked prin- 

 cipally from the lower surface through the stomata ; (6) the injury is probably 

 caused by the excess of carbon dioxid evolved in the shade passing into the 

 water standing on the surface of the leaf during wet weather, the carbonated 



