406 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Pear-Tree, Canker. By V. Enfer (Rev. Hort. vol. xci. pp. 217, 218). — Canker 

 in pear-trees may be cured by scraping the diseased part and then painting 

 the wound -with a strong solution of sulphate of iron containing 1 per cent, of 

 sulphuric acid (53 0 Baume). — S. E. W. 



Pemphigus populi-transversus, Life History of. By T. H. Jones and C. P. 

 Gillette [Jour. Agr. Res. xiv. pp. 577-594, Sept. 23, 1918 ; plates). — A full 

 description of this Aphis is given, together with its life history. 



It has been proved that this species feeds on the roots of Crucifers, as well as 

 causing galls on the leaf-petioles of some of the Poplars. The galls begin to 

 develop in spring and increase in size during the summer. By the autumn they 

 have often reached the diameter of nearly an inch. 



The presence of the Aphis on the roots of Crucifers may be easily detected, as 

 they cover themselves with white cottony material. 



Dr. Gillette completes the paper by giving detailed descriptions of the Aphis 

 in all its forms. — G. F. W. 



Permeability, A New Method of Studying. By S. C. Brooks (Bot. Gaz. 

 vol. lxiv. No. 4, Oct. 1917 ; pp. 306-317; with 2 figs.). — The writer describes a 

 method of studying permeability, which depends upon the diffusion of salts or 

 other substances through a diaphragm of living tissue, viz. portions of the 

 frond of Laminaria Agardhii — one of the common sea-weeds of the New England 

 coast. 



The apparatus used consists of two artificial cells, constructed from glass 

 tubing, containing the fluids under investigation. The two open ends of the 

 tubes were placed together and separated by a piece of prepared tissue. Changes 

 in concentration of the solutions in each cell were measured by determining the 

 changes in electrical conductivity. 



As the result of a series of experiments it was found — 



(1) That the protoplasm of Laminaria is normally permeable to the salts of 

 sea-water. 



(2) Sodium salts cause an increase of permeability which 'culminates in 

 death. 



(3) Calcium and lanthanum salts cause a decrease in permeability, followed 

 by an increase which culminates in death. — R. J. L. 



Permsability of tb.3 Call Walls of Allium. By S. C. Brooks [Bot. Gaz. vol. 

 lxiv. No. 6, Dsc. 1917 ; pp. 509-512). — The impermeability of the tissues of 

 higher plants to inorganic salts has usually been attributed to the impermea- 

 bility of the protoplasm to the salts used. The investigations of the writer 

 show that in certain cases the influence of the impermeable cell wall is an important 

 factor. He found that the exterior cell wall of the epidermis from the inner 

 surface of onion bulb scales is slightly permeable to hydrochloric acid, while it 

 is practically impermeable to various salts and dyes, and to caustic soda. These 

 results were obtained by experiments conducted on the same principle and 

 with the same apparatus as was used in the writer's experiments on Laminaria 

 (vide Bot. Gzz. same volume; pp. 304-317). — R. J. L. 



Permeability, Methods of Studying Permeability of Protoplasm to Salts. 



By C. S. Brooks (Bot. Gaz. vol. lxiv. No. 3, Sept. 191 7 ; pp. 230-249). — 

 The writer sets out to consider critically the methods hitherto employed in the 

 study of permeability in order to determine which of the methods can be con- 

 sidered most reliable and help most towards the solution of the problem. He 

 concludes that the steps most essential to further progress are : (1) A thorough 

 analysis of the various disturbing factors in the methods involving chemical 

 determinations, and the satisfactory interpretation of the results secured by 

 such methods ; (2) the same type of analysis of the methods depending on 

 turgor, with special reference to the possible effect of exosmosis ; and (3) the 

 establishment of methods of determining progressive changes in permeability 

 without the various disadvantages of the other methods. — R. J. L. 



Physodermi Disease of Indian Corn (Zea Mays). By W. H. Tisdale (U.S.A. 

 Jour. Agr. Res. xvi. No. 5, Feb. 1919, pp. 137-154 ; 10 plates). — The Physo- 

 derma disease was first discovered by Shaw (1910) and Barrett (191 1). 

 It occurs practically throughout the corn-growing areas of the U.S.A., and is 

 particularly prevalent in Atlantic and Gulf Coast States and in the Mississippi 

 Valley. The causal organism is Physoderma Zeae maydis Shaw, and its develop- 

 ment is favoured by moist, warm weather. The sporangia of the fungus live 

 over the winter on old diseased plants and also in the soil, and germinate the 



