148 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



N. Jersey Agr. Exp. Stn. Feb. 1916), but the authors believe the apparent 

 discrepancy to be due to a misinterpretation by Richardson of his own experi- 

 ments. They found that carbon dioxide was the inciting substance and not 

 ammonia as stated by Richardson. A comparison of the total number of eggs 

 laid under similar conditions expressed as " per cent, of total unit average " 

 between CO, and ammonia gives the figures 91-4 against 8 6. The controls 

 compared with CO., in the same way show very similar results, 92*4 to 7-6. — 



G. W. G. 



Hybridization and Cross-fertilisation of Flowers. By J. Heal (Gard. Chron. 

 Jan. 18, 1919, p. 25). — A very interesting record of successes and failures in 

 crosses achieved and attempted between a great number of plants. Many 

 of the experiments were between distinct genera. Many Begonia, Primula 

 and Anthurium crosses are given. — E. A. B. 



Hydrocyanic Acid Gas as a Soil Fumigant. By E. R. de Ong {Jour. Agr. 

 Res. xi. pp. 421-436, Nov. 19 17 ; plates). — The use of hydrocyanic gas as a 

 soil fumigant is restricted on account of the damage it does to plants and seeds 

 of the amount retained by clays, and the difficulty and slowness of diffusion in 

 wet soils. It may be used in " masses of loose, porous soil, especially those with 

 only small amounts of clay, or of seed beds and potting soil. Such treatments 

 allow of much wider range of concentrations when the soil is not occupied by a 

 crop." Hydrocyanic acid does not therefore appear to be a suitable fumigant 

 for use outdoors. The amounts of sodium cyanide required for an acre varied 

 very much in different soils, viz. from 483 lb. in a gravelly soil to 3,030 lb. in a 

 clay loam where Phylloxera on vines was the pest aimed at, and the gas was 

 required to penetrate to a depth of 3 feet. — F. J. C. 



Hydrocyanic Acid, Greenhouse Fumigation with. By W. Moore and J. J. 

 Willaman (Jour. Agr. Res. xi. pp. 319-338, Nov. 1917 ; plates). — Tomato plants 

 fumigated with hydrocyanic acid absorb more or less of the gas ; the immediate 

 effect of the presence of this poison is reduction in oxidase and catalase and 

 therefore in respiratory activity, followed by stoppage of photosynthesis and 

 translocation of carbohydrates and closing of stomata. The cell-walls become 

 more permeable, leading to less rapid intake of water from stem and greater loss 

 through cuticle, so that wilting follows. Where fumigation is mild, recovery 

 is more or less rapid, and oxidase activity returns to normal, while catalysis 

 exceeds normal and respiration may remain above normal for some time. Other 

 functions somewhat slowly regain normal, but may in time exceed it, and in- 

 creased growth may occasionally follow. — F. J. C. 



Insect Injury, Prevention of (Quart. Jour. For. July 1918). — The Council of the 

 Arboricultural Society desire to draw attention to the very serious risk of the 

 increase of destructive forest insects in consequence of the extensive fellings that 

 are going on all over the country. Mr. M. C. Duchesne, in the last issue of the 

 Journal, indicated preventive measures in the case of the pine Weevil, but there 

 are many other injurious insects that are likely to become exceedingly abundant 

 unless precautions are taken. Species of Pissodes, notably P. pini and P. notatus, 

 the Pine Beetle (Hylurgus piniperda), the Ash Bark Beetle, and the Elm 

 Bark Beetle, are cases in point. These all breed in the top and lop and in the 

 stools of felled trees, and from these breeding places the new broods make their 

 way to growing trees, which they may severely cripple and ultimately destroy. 

 The best way to prevent their increase is to see that all brushwood is burned 

 not later than April of the year succeeding the autumn or winter of felling. 

 As far as possible the fires should be made on the stools, for in this way the latter 

 may be made to a large extent unsuitable for the insects breeding. To leave 

 brushwood lying in the woods during the summer is a most reprehensible practice, 

 which might very well be the subject of a Government Order. 



Light and Air in Relation to Tree Growth. — Light and air are the dominating 

 factors of tree growth. Trees, like animals, must feed and breathe in order 

 to live : the tree-food consists of two kinds — water and gas. Water is absolutely 

 essential for the life of the tree, both as a direct food and as a medium to convey 

 inorganic food from the soil to the leaves. Of the organic elements, the carbon 

 is obtained from the carbonic acid gas absorbed by the leaves from the air together 

 with some oxygen, while the rest of the oxygen and the nitrogen and other 

 elements are obtained from the soil in the form of nitrates, phosphates, or 

 sulphates dissolved in water. 



If trees of good girth are required at the end of the rotation, after this first 

 weeding out it is necessary to assist them by thinning. This may have to be 

 done at any time from ten to twenty-five years old, depending on the species 

 and ra'e of growth. This operation should be very Ught, because if the trees 



