DISEASES OF PLANTS. 351 



spores (iff on other parts. The remedies advised are frequent picking of the 

 rii)e figs, Iceeping the ants out of the trees) by means of ant tape, etc., and by 

 planting varieties not readily susceptible to the disease, such as Celeste and 

 Reine Blanche. 



The fig rust is a very common disease, and usually defoliates the trees in 

 the late summer. No treatment for it is known. Leaf spot and die-back are 

 of little economic importance so far, while the root galls due to nematodes 

 are often quite troublesome in sandy soils but of little importance in sticky, 

 clayey soils. A 3-year rotation with other crops is said to control this disease. 



A bibliography is appended. 



The American gooseberry mildew order of 1909, T. H. Middleton (Bd. 

 Agr. and Fisheries [London], Intel. Div., Ann. Rpf. Proc. 1909-10, pp. 73-76). — 

 This order in regard to the control of the American gooseberry mildew is 

 printed in full. It includes directions as to notification of the disease, in- 

 vestigations and action by local authorities, precautions to be observed against 

 the spread of the disease, a prohibition of the importation of the bushes, the 

 powers of boards and inspectors, and penalties under the act. 



The influence of the stock on the susceptibility of the graft to grape 

 mildew, L. Ravaz (Prog. Agr. et Vit. (Ed. VEst-Ccntre), 32 (1911), No. 19, 

 pp. 598-600). — The author claims that in grapes where the union between scion 

 and stock is perfect, resulting in a vigorous, succulent growth, the suscepti- 

 bility is increased, while the reverse is true of unions in which there is not a 

 perfect affinity between scion and stock, resulting in a less vigorous and 

 therefore less watery condition of the foliage and young shoots. 



The method of the action of sulphur used in combatting' powdery mildew, 

 R. Marcille (Compt. Rend. Aead. Sei. [Paris], 1.52 (1911), No. 12. pp. 780-783).— 

 The author claims that experiments have not been carefully conducted in 

 determining the manner in which sulphur acts as a fungicide, and he has 

 carried on some experiments in Tunis to settle this point. 



It has generally been asserted that the sulphur acts through its volatilization 

 or oxidation, but the author found that under the conditions of his experi- 

 ments these two functions were of very little importance. He claims that 

 sulphur used for the prevention of powdery mildew owes its efficiency to the 

 sulphuric acid which it contains. Pure sublimed sulphur was found to contain 

 from 0.2 to 0.625 per cent anhydrous sulphuric acid. The sulphuric acid which 

 the sulphur contains under ordinary conditions does not injure the tissues of the 

 plant, but when, through condensation of humidity, the conditions favor the 

 development of mildew, the small drops which form dissolve the acid and 

 impregnate the spores and mycelium of the fungus, which are killed through 

 the concentration of the acid due to evaporation of the solution. 



This hypothesis, it is said, explains particularly the efficiency of the extra 

 sublimed sulphurs, as they contain notable quantities of sulphuric acid, while 

 the ordinary and triturated forms of sulphur contain it in very small amount. 



The author thinks that for use as a fungicide sulphur should be prepared in 

 such a way as to contain a greater amount of sulphuric acid than that which is 

 ordinarily furnished. 



The black-rot disease of grapes, D. Reddick (New York Cornell Sta. Bui. 

 293, pp. 289-364, pis. 5, figs. 16). — This is a comprehensive discussion of the 

 black rot of grapes, based in part on original investigations by the author, in- 

 cluding a histoiy of the disease, the geographical distribution, economic im- 

 portance, symptoms, name and life history of the parasite, and the meteorologi- 

 cal relations, incubation period, period of susceptibility, longevity of pycnospores, 

 pathological histology of the leaf, stem, and berry, and the methods used for 

 controlling this disease. 



