DISEASES OF PLANTS. 163 



The action of copper on leaves, S. M. Bain {Ihme^see Sta. BuL, Vol. XV, 

 No. 2, iH'. 21-108, ph. 8, fig. 1). — This bulletin gives the results of investigations 

 begun in 1895 and continued with some interruption until 1901, a preliminary 

 account of which has already been given (E. S. E., 13, p. 866). The object of the 

 experiments was to ascertain the effect of fungicides on peach foliage, which might 

 be of economic value in the treatment of the diseases of that plant. Comparative 

 studies were made on the effect of fungicides on apple and grape. The poisonous 

 action of copper solutions introduced through the roots, the action on tlie leaves and 

 conditions affecting the action, the permeability of the cuticle of the leaf and its rela- 

 tion to the action of fungicides, wound healing of the leaves and leaf fall, and the 

 influence of copper on the assimilative function of leaves are all discussed at con- 

 siderable length. 



From the evidence presented there appears to be little doubt that copper is 

 absorbed by the leaves of plants sprayed with Bordeaux mixture. The conclusive 

 and final evidence of the entrance of co^^per into the tissues of the leaf is a subject 

 for future investigation. One of the first conditions permitting the absorption of any 

 substance by the leaf is that the substance shall ])e either a liquid or dissolved in a 

 liquid. The injury to peach foliage caused by copper is the same whether supplied 

 in the form of a soluble salt or an insoluble hydrate. There appears to be some sub- 

 stance escaping from the peach leaf which has a solvent action on copper hydroxid, 

 but the nature of this substance is as yet not known. It is shown that while peach 

 leaves are able to dissolve copper hydrate, the presence of lime has a tendency to 

 prevent this solvent action and retards or wholly prevents the injury of copper to the 

 leaves. One of the most important features in tljis connection is the solubility of 

 copper applied to the leaves. Attention is called to the action of the so-called strong 

 and weak Bordeaux mixtures. If properly made, these differ only in the amount of 

 copper hydrate deposited upon the leaves. An excess of lime in Bordeaux mixture 

 has a tendency to retard the rate of the entrance of copper into the leaf Ity simply 

 jireventing the copper from passing into solution. Another important factor con- 

 trolling the entrance of copper into the leaf is the presence of water. It is shown by 

 the author's experiments that no injurious effect follows the spraying of peach leaves, 

 providing they are not exposed to rain or dew. Another factor to be considered is 

 the rate of entrance of the copper into the leaf through the permeability of the leaf 

 cuticle. 



Sunnning up his investigations, the author concludes that peach foliage is very 

 susceptible to injury by fungicides because the leaves are especially sensitive to poi- 

 sons in general and to copper in particular. Peach leaves have the power, which 

 may or may not be possessed by other leaves, of dissolving copi^er hydroxid. They 

 have a cuticle which is thinner and more permeable than many other leaves, and 

 the glandular surfaces terminating their marginal teeth are especially fitted for the 

 absorption of copper in solution by reason of their thin cuticular covering. Peach 

 leaves are especially sensitive to the various agencies producing leaf fall by the pro- 

 duction of a normal abscissal layer. They have the power, in common with other 

 leaves of the same genus, to exfoliate any injured region, and this involves much 

 more than the really injured cells. If this process removes a large portion of the 

 lamina, the whole leaf falls. As a practical suggestion for the prevention of injury 

 the author recommends the spraying of leaves with a thin solution of milk of lime 

 about 2 days in advance of the spraying with Bordeaux mixture. This will offer 

 considerable protection to the leaves against the injurious action of the copper, and 

 the Bordeaux mixture lying above the stratum of calcium carbonate can act upon 

 any fungus spores coming in contact with it. An extensive bibliography on the 

 subject concludes the bulletin. 



Some recent ■work -with, fung-icides by the experiment station, A. D. Selby 

 [Proc. Columbus Hort. Soc, 16 {1901), jyp. 1S4-186). — A report is given of experiments 



