554 EXPERIMENT STATION RECORD. [Vol.38 



before the close of the growing season from two to four times the size of those 

 on the untreated beds. 



How to preserve the oaks, L. Daniel {Compt. Rend. Acad. Sci. [Parts], 164 

 (1917), No. 25, pp. 957-959). — The injury done to oalis by mildew since 1908 is 

 attributed largely to the defective methods of lopping in vogue, the resulting 

 changes in the form of the tree and the disturbance of equilibrium between the 

 fundamental processes culminating in a greater degree of susceptibility. 



Hevea canker, III, A. A. L. Rutgers (Dept. Landb., Nijv en Handel [Dutch 

 East Indies], Meded. Lab. Plantensiekten, No. 28 {1917), pp. 49, pis. 12, figs. 

 2). — Reporting further (E. S. R., 37, p. 458) on Hevea canker, the author states 

 that the stripe canker, which shows a decay of the renewing bark and appears 

 only during the very wet weather of the rainy season, may be induced artifi- 

 cially by applying conidia suspended in water to the wounds made by tapping. 

 The black lines enlarge and may so fuse as to cover the whole surface of the 

 renewing bark. Tran.sition stages between stripe canker and ordinary canker 

 may be found. The disease may spread with exceptional rapidity where tap- 

 ping is kept up or where water is used on the tapping cuts. Carbolineum, 

 formerly used as an antiseptic at 50 per cent concentration, is now used at 20 

 per cent, and it is thought that this may be safely reduced perhaps to 5 per 

 cent. 



Both forms of canker are due to Phytophthora faberi. Canker patches of the 

 ordinary sort are produced by inserting mycelium into an incision in the old 

 bark. Bur formation of a certain sort described is regarded as a symptom 

 of canker. Under favorable circumstances the trees recover from light attacks 

 provided tapping is stopped. 



The Phytophthora forms from Hevea, cacao, and nutmeg are said to belong 

 to the same species. The strain from cacao is more virulent for that host and 

 for Hevea, and the nutmeg strain for its own host. Comparisons of pure cul- 

 tures are said to show that morphologically the four forms P. faberi, P. nico- 

 tianw, P. colocasice, and P. jatrophw are distinct species, the last named being 

 of the type of P. infestans, and P. fagi and P. cactorum being quite different 

 from the others. 



Preventive measures considered as most important for canker include thin- 

 ning, drainage, and removal of Intercrops, pruning having been abandoned. 

 Direct measures include cutting out the red patches of canker and the appli- 

 cation of carbolineum to the stripe cankers. The disease should be detected 

 early and tapping stopped. 



It is thought from very recent experiments that stripe canker can be pre- 

 vented entirely. P. faberi can attack unwounded fruit, causing a rot which 

 may spread very rapidly. Drosophila appears to be an active agency in 

 spreading the disease. The burs found on Hevea trunks may be the result of 

 leaf scars, pricking, or canker. Of the last named there are two forms, one 

 deep-seated, the other due to secondary wood formation in the cortex and 

 curable by stopping the tapping and treating the cankers. 



Abnormal leaf fall of Hevea rubber, W. McRae {Planters' Chron., 11 

 {1916), No. 37, pp. 459-465) .—This is a report of a lecture before the United 

 Planters' Association of South India in which the speaker discussed some pre- 

 liminary studies of a disease which is now attributed to a Phytophthora 

 hitherto but little known on rubber plantations, having been first mistaken for 

 P. faberi. The effects of the disease on the different parts of the plant are 

 described. It was first definitely noted as a fruit rot, but is now also charac- 

 terized by an abnormal shedding of leaves from June to August. 



