148 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Acacias, An Economic Study of. By C. H. Shinn (U.S.A. Dep. Agr., Bull. 

 9, December 5, 1913). — The Acacias are so valuable as a source of tanning 

 material and of timber, and so well adapted to the reclamation of sandy semi- 

 desert lands, that their introduction into parts of the United States may prove 

 profitable. 



They are in the main, natives of Australia, which has about 300 species. 

 There are 150 other species scattered over the world, principally in Asia, Africa, 

 and America, with one important species, the Koa, in the Hawaiian Islands. Of 

 the 450 not more than 75 have a known economic value, and not more than 50 

 are in general cultivation, though 150 species are growing in nurseries, gardens, 

 and arboreta in the United States. 



So far as is known, no other semitropic trees of high economic value possess 

 to as great an extent the ability to thrive upon and to improve a great variety of 

 arid and sterile soils. Through their agency large areas of land unfit for ordinary 

 cultivation, and at present producing only a scanty pasturage at best, may be 

 reclaimed and utilized. Recent discoveries in the nitrogen-fixing qualities of 

 the legumes point to the possibility of a hitherto unrecognized value in Acacia- 

 growing. 



Some Acacias have a remarkable value for the reclamation of sand dunes, 

 whether they are seashore drifts or inland barrens. 



Many species furnish tan-bark ; others yield forage ; others produce timber of 

 notable quality ; almost all are suited to ornamental plantings, many are 

 excellent for street trees and tor shelter belts, and several furnish many special 

 products of great economic value. — A. D. W. 



Acid and Alkaline Solutions, The Effects of, upon the Water Relation and the 

 Metabolism of Plants. By Alfred Dachnowski (American Jour, of Botany, vol. i. 

 No. 8, Oct. 1914, pp. 412-440 ; 4 figs.). — A series of experiments was devised to 

 determine what importance hydrolytic reactions may have in regulating and 

 determining the amount of water absorbed and retained by plants during 

 germination and growth. Both seeds and cuttings of plants were used. 



The chief conclusions arrived at were : — 



1. Seeds of Phaseolus multiflorus swell more and retain greater quantities 

 of water in the solution of any acid than in distilled water. 



2. The amount of water that seeds absorb and retain in an acid solution 

 is not dependent upon the concentration of the acid and is not a function of it. 



3. When equinormal acids are compared the amount of water retained is 

 greater in sulphuric acid than in hydrochloric or in nitric acids. The first 

 two acids are about equally dissociated and yield a greater concentration of H 

 ions than the equinormal nitric acid, but the amount of water retention induced 

 seems to be determined not by the concentration but by the ^anions of the parti- 

 cular acid. The order of effectiveness of the anions in accelerating the water 

 content is S0 4 , CI, and NO s . 



4. The addition of any salt to a solution of HC1 w/800 does not decrease the 

 quantity of water absorbed or retained by seeds of Phaseolus. The amount 

 retained is increased if K 2 S0 4 is added. A higher concentration of any salt is 

 followed by inhibition in the capacity for absorbing and retaining water. In a 

 series of salts having a common anion, the order of effectiveness of the kation 

 is K, Na, and Ca, the ion most effective being placed first. 



5. The conclusions on the absorption and retention of water by seeds in the 

 alkaline solutions are the analogue of those for the acids. Seeds of Phaseolus 

 multiflorus absorb and retain more water in solutions of any alkali than in distilled 



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