222 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
3. The stimulating effect of cold is limited to such portions of the plants 
subject to the chilling. 
4. The stimulating effect on dormant plants^by cold is intimately associated 
with the transformation of stored starch into sugar. The author suggests that, 
in the process of chilling, the starch grains are separated by the living cell from 
the enzyme, which would act upon it and convert it into sugar ; but when the 
plant is chilled the vitality of the cell is weakened, so that contact between the 
starch and the enzyme takes place and converts it into sugar. 
5. The twigs of trees and shrubs after their winter chilling and the transfor- 
mation of their starch into sugar may be regarded as mechanisms for the develop- 
ment of high osmotic pressures which cause the plant to grow. The dormancy 
before winter and during winter are protective adaptations of vital necessity to 
the native trees and shrubs. This principle of chilling is essential to an under- 
standing of plant breeding and propagation. — A. B. 
Plum, Mealy Aphis, Life-history and Habits of the. By W. M. Davidson 
(U.S.A. Dep. Agr., Bull. 774, April 1919 ; 2 plates). — The mealy plum aphis 
(Hyalopterus arundinis Fab.) is a pest of plums, prunes, and, to some extent, 
apricots in California. Besides devitalizing the trees it causes small fruit, and 
is probably concerned in a measure with apical cracking of prunes. — V. G. J. 
Poison Gas for Pest Extermination (Agr. Gaz. N.S.W. xxxi. pp. 13-15).— 
Rabbits can be exterminated by means of phosgene gas, which is conveyed 
into the burrows by pipes from cylinders of the gas. It is also suggested that 
flying foxes may be destroyed by projecting the gas upwards to their sleeping 
lairs. On account of its destructive action on crops and animals the operation 
must be conducted with the greatest precautions. — 5. E. W. 
Poplar Longhorn, The Large, Saperda Careharias Linn., The Structure, 
Bionomics and Economic Importance of. By W. Ritchie (Ann. App. Biol. 
vii. Nos. 2-3, pp. 299-343 ; 25 figs., 3 plates).— A very complete account of the 
life-history of this serious pest of forest trees. 
In the larval stage this insect does an immense amount of damage by boring 
in the stems, and occasionally tunnelling into side branches ; while the adults 
feed upon the leaves. 
Several species of Poplar are recorded as hosts for this beetle, but the Aspen, 
Populus tremula, is the commonest. 
Detailed descriptions are given of the egg, larva, pupa, and adults. 
The remedies recommended are (1) to cut and burn all infected trees by the 
end of June each year, before the beetles begin to emerge ; (2) when the adults 
are present, easily determined by the cutting of the leaves of the host plant, 
they should be sought out and collected ; and (3) in the case of park trees, 
oviposition may be prevented by ensheathing the lowermost portions of the 
stems, about i£ feet above the level of the ground, with close mesh netting, 
or by painting the trunks with a repellent wash. 
The only natural eremy found was an Ichneumonid larva, which attacks 
the Saperda larva while boring the horizontal portion of its gallery. — G. F. W. 
Potassium Cyanide for Trapping Fruit Flies. By A. A. Ramsay (Agr. 
Gaz. N.S.W. xxxi. pp. 821, 822). — Aqueous solutions of potassium cyanide 
decompose more rapidly when exposed to light than in the shade. As a one per 
cent, solution is decomposed in eight days, it should be renewed twice a week to 
be efficient. — S. E. W. 
Potato, "Blackleg" Disease of. By E. F. Artschwager ( U.S.A. Jour. 
Agr. Res. xx. No. 4, Nov. 1920, pp. 325-330 ; 2 plates). — Blackleg is a 
bacterial disease affecting the underground stem and tubers of the potato, and 
has been described by Appel, Smith, and Morse. Typically, the attacked stem 
may show blackening above the ground for some inches, the foliage is discoloured, 
usually light, with a metallic lustre. In the latter stages of the disease the whole 
plant turns brown and decays away. 
The histological changes consist in a great increase of strongly lignified 
vascular tissue and transformation of pith and cortex into sclereids. Protein 
crystals are also formed in leaves, stems, and tubers. These changes have been 
observed only in diseased plants grown in the arid western sections of Colorado. 
Possibly in other parts of the U.S. diseased plants will not show these 
anatomical changes. — A . B. 
Potato: Effects of Reot and Nc-Rest Periods upon Growth of Solanum. 
By W. F. Gericke (Bot. Gaz. vol. lxv. No. 4, April 191 8, pp. 344-353). — The 
author investigated the effect of various rest periods of the tuber upon the 
subsequent growth of the plants. He found : 
