igo JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Thorn Formation, Cause of. By A. Lothelier {Rev. gen. de 

 Bot. t. 24, pp. 297-7). — Since the earlier work of Lothelier (1893) 

 on the production of thorns in plants, it has been generally believed 

 that the development of these structures is favoured, or even caused, 

 by atmospheric desiccation or by intense light, or both factors acting 

 together. Lothelier found that in the common gorse [Ulex europaeus) 

 the branches of the second order, which normally end in a sharp spine, 

 grew out to form leafy shoots when caused to grow in humid air or 

 in feeble light ; he obtained similar results with Berberis, Crataegus, 

 and other spiny plants. Cockayne (1905) obtained similar results 

 with Discaria Toumatou, a New Zealand Rhamnaceous plant ; spines 

 were not developed in moist air and feeble light, their place being 

 taken by leafy shoots of unlimited growth. Zeidler (1911) found 

 that thorns were developed in Ulex plants kept in partial darkness 

 or in moist air, and he regarded the leafy shoots obtained by Lothelier 

 under similar conditions as being merely juvenile forms, the thorny 

 shoots being adult forms. However, even if these results of Zeidler's 

 be accurate and we accept his view instead of LotheHer's, it is obvious 

 that it still remains to be determined why " juvenile shoots " should 

 appear at some times and " adult shoots " at others. Lothelier 

 now replies to Zeidler's criticism, and states that if the leafy shoots 

 are produced only in moist air the latter must surely be considered 

 as the cause of their production ; hence, if Zeidler's view is correct, the 

 leafy " juvenile " form ought to become spiny towards the growing 

 end, whereas as a matter of fact this transformation does not take 

 place in moist air. He therefore maintains his former view that 

 atmospheric humidity is the direct cause of the inhibition of spine 

 development in a normally spiny plant like Ulex, and conversely that 

 the production of spines is the direct result of desiccation and strong 

 illumination. It is clear that further investigation is necessary for 

 a solution of what appears at first sight a simple matter, but which 

 in reality is very complex. — F. C. 



Tomato, Black Spot. By G. P. Darnell-Smith {Agr. Gaz. N.S.W. 

 vol. XXV. pt. i. p. 26). — Some varieties of Tomato are more free from 

 black spot than others. Spray the plants with Bordeaux mixture 

 as soon as the blossoms fall. Irregular watering, too much exposure 

 to the sun, and too much nitrate of soda predispose the plants to 

 attack by Black Spot. — 5. E. W. 



Transpiration of Infected Apple Leaves. By H. S. Reed and 

 J. S. Cooley {Boi. Gaz. June 1913, pp. 421-430 ; i fig.). — ^The authors 

 give tables of observations of the transpiration of apple leaves infected 

 with Gymnosporangium. The shoots with a few apple leaves were 

 enclosed in a glass cylinder and the exhaled water absorbed with 

 calcium chloride. The experiments lasted from July 9 and 11 to 

 August 20 and 23. They found that the transpiration of diseased 

 leaves was almost always less than that of healthy ones. Yet at 



