DISEASES OF PLANTS. 749 



togetlier and more or less confluent. Generally they appear along the middle of 

 the leaf, the edges, tips, and petioles being free. The differences in color are- 

 very slight while the leaves are attached to the plant, but upon curing the gi-een 

 areas become conspicuous. A microscopical examination of the leaves showed 

 a decided thickening of the mesophyll in the areas that remained green as com- 

 pared with the normal leaf. The disease seems most prevalent on the so-called 

 oriental varieties of tobacco. The cause of the trouble appears to be not 

 definitely determined. 



Preliminary note on silver leaf disease of fruit trees, H. T. GiJssow (Pliy- 

 ioitatholooii, 1 (1911), Xo. 6, pp. 111-119, pi. 1). — The author reports observing 

 in Nova Scotia in November, VM)%, the first authentic case of the silver leaf 

 disease in America. He has since found about GO trees affected by this disease 

 in different localities. Although in Europe a number of species of plants are 

 known to be attacked, so far only plums and apples have been so noted in 

 Canada. Records are given of the disease in various countries, and the author's 

 observations seem to confirm those of Pickering that the disease is due to the 

 fungus Stereiim purpureum (E. S. R., 24, p. 349). 



Some frost injuries of fruit trees, G. Lustner {Dent. Obsthau Zip., 1912, 

 No. 3, pp. .50, Gl, fKjs. 2). — Pursuant to a former article by him (E. S. R.. 25, 

 p. 847), the author briefly describes some injuries by freezing to apple, pear, 

 plum, peach, and apricot trees in various parts of Germany. The younger trees 

 were the worse damaged. Some young fruits of injured trees showetl a dis- 

 position to split, generally from the calyx outward, the wounded surface later 

 forming a layer of cork-like material from the exposed tissue. 



Remedy for chlorosis or tip burn in fruit trees {Bol. Quind. Soc. Agr. Ital., 

 16 (1911), No. 16, p. 595; ahs. in- Mitt. Dent. Landiv. Gesell., 26 (1911), No. .',2, 

 p. 5S2). — The use of iron sulphate is recommended. In May or June a hole 

 should be bored slantingly downward to the center of the trunk of a diameter 

 equal to one-tenth of its depth. This should be packed full of the powdered 

 crystals and sealed with wax. 



The effects, it is stated, usually appear in a few days in the complete yellow- 

 ing and fall of the leaves most affected (these being soon replaced by young 

 healthy foliage), and the rapid recovery of color in neighboring leaves and 

 twigs. If some remain yellow, it is advisoble to repeat the treatment in the 

 following year. Occasionally a third annual treatment is found to be necessary. 



Investigations on the growth and spread of decay fungi in. storage fruit, 

 O, ScHi\EiDF:R-ORELLi {Ldudir. JaJirJ). ^clnveiz, 25 (1911), No. 3, pp. 225-2'i6; 

 Centbl. Bakt. [etch 2. AM., 32 (1912), No. 6-12, pp. 161-169).— The author gives 

 the results of his investigations on fruit rots caused by various organisms under 

 different conditions. The principal forms studied were Penicillium glaucum, 

 Botrytis cinerea, Monilia fnictigena, Gloeosporium fructigennm, G. a1t)um, 

 Fusarium- putrefaciens, Cladosporium herharum, Mucor piriformis, Rhizopiis 

 nigricfiiis, and a few others. Quantitative results are given as to rapidity of 

 growth in cultures of different temperatures, the progress of each fungus with 

 each of several varieties of fruir, and the germ content of the air in fruit 

 cellars or in the open, with some observations by the investigator. 



Stored fruit is subject to many factors as to the preservation of its freshness. 

 Prominent among these are (1) the natural life period of the cells (varying 

 with variety, ripeness when picked, etc.), (2) the activity of the rot fungi 

 (affected by temperature and by the water content of the air and fruit), and 

 (3) injuries; these being closely interrelated. While M. fructigena is very 

 common on unripe and tree-ripe fruit, P. glaucum appears to be the chief cause 

 of rot in the fruit cellars. B. cinerea seems to work more rapidly in the fruit 

 body when once started, and M. piriformis and B. nigrxcQ/ns are common rots of 



