NOTES AND ABSTRACTS. 



149 



are opened out much at this stage, coarse and branchy timber will result. If 

 the plantation is pure coniferous, the operation is comparatively simple, for all 

 suppressed and confined trees should be cut out, due care being taken not to 

 break up the canopy. If the crop is of mixed conLers and hardwoods, the 

 more valuable trees should be given somewhat more room by cutting out some 

 of the less valuable that are pressing cn them. The slower-grovnng valuable 

 species must be assisted against those that are quicker-growing and less valu- 

 able, while extra large individuals of a branchy nature should be kept in close 

 confinement. 



If the wood is thinned too much in its ear'y life, it will, in the course of time, 

 if left alone, recover to a certain extent, provided the trees are in a healthy 

 condition. The writer has seen an almost pure wood of sycamore about thirty 

 years old, which some ten years previously had been very heavily thinned, 

 with the result that the trees became verv branchy. 



Trees on the edges of woods are naturally always inclined to branch on 

 their exposed sides, but if the wood happens to be affected with the larch aphis 

 or larch canker fungus (Peziza Willkommii) these trees will almost always be 

 healthy and free from infection. This implies that these diseases are not prevalent 

 when the trees are given plenty of air and light. — A. D. W. 



Laeliocattleya x elegans. By R. A. Rolfe (Orch. Rev. xxvi. 1918 ; pp. 252-254). — 

 A chronological history of this well-known natural hybrid from the time when it 

 was originally described as a species of Cattleya, in 1848, until it was raised artifici- 

 ally by Mr. E. F. Clark, from Cattleya Leopoldii x Laelia purpurata, over sixty 

 years later. The history of its long confusion with another natural hybrid, now 

 known as Laeliocattleya x Schilleriana Rolfe, and which has been raised artificially 

 from Laelia purpurata x Cattleya intermedia, by Mr. Chas. Morrow, is also 

 given. — R. A. R. 



Lead Arsenates, Stone Fruits, and the Weather. By Geo. P. Gray (Jour. 

 Econ. Entom. vol. x. pp. 385-392, Aug. 1917). — The two types of commercial 

 lead arsenate are discussed. The acid type (lead hydrogen arsenate, often labelled 

 " Standard ") is the stronger and quicker acting, but is not so safe in use as the 

 basic lead arsenate (usually labelled " Neutral "). The latter is the one to be 

 recommended whenever an arsenical is mixed with others to form a combina- 

 tion spray ; and should also be used in humid regions and upon all stone 

 fruits. Acid lead arsenate would be selected in more arid regions, and for use on 

 foliage not peculiarly susceptible to spray injury. — G. W. G. 



Lettuce Anthracnose caused by Marssonina Panattcniana. By E. W. Brandes 

 (Jour. Agr. Res. vol. xiii. No. 5; pp. 261-280; 2 plates). — The symptoms 

 of the disease are distinct lesions on the leaf blade and midrib. This causes 

 much dwarfing and wilting of the leaves. The organism (Marssonina Panattoniana, 

 M. perforans) has been proved to be the cause of this disease. The author finds 

 that the spores produce germ tubes in about six hours and can penetrate through 

 the epidermis. Germination of the spores cannot take place above 32°C. The 

 spores can withstand desiccation on glass for only four days. The fungus cannot 

 grow at temperatures above 3o°C, the thermal death-point being 40 0 for ten 

 minutes. A short bibliography is appended. (See Journal R.H.S. xxxvii. 

 p. 541.)— A-B. 



Lettuce, Some Bacterial Diseases of. By N. A. Brown (Jour. Agr. Res. 

 vol. xiii. No. 7, May 1918 ; pp. 367-388 ; 14 plates). — Two new bacterial diseases 

 of the lettuce are described. One occurs in South Carolina and Virginia, while 

 the other was found in Kansas. The first attacked the stems and the roots, 

 while the Kansas disease attacked chiefly the leaves. An infectious bacterium 

 was isolated from the attacked plants, and the name Bacterium vitians (n.sp.) 

 is suggested. The group number 211.3332523 of the Society of Bacteriologists' 

 Chart is assigned to the organism. 



The Kansas disease is attributed to Bacterium marginale (n.sp.), with a group 

 number 21 1.2323 123 of the Chart. 



Bacterium marginale causes decay of the margins of the inner whorls of leaves 

 of immature plants, but occasionally the infection spreads over the whole leaf 

 surface. The organism is mobile, possessing one or two polar flagella, is Gram- 

 negative and not acid-fast ; may be grown readily in most of the commoner 

 media, and can retain its vitality for more than one year. 



Bacterium vitians is not actively motile, and may occur singly, in pairs, or in 

 short chains. It is Gram-negative and is not acid-fast. The growth of the 

 organism was most pronounced on potato cylinders, where it formed a bright 

 yellow slimy growth. Beef bouillon and litmus milk were also favourable media 

 for prolonged growth. — A. B. 



