JEHANGIR PARDUNJI DASTUR 227 



that it is identical with the " Black Thread " disease of Hevea in Burma. The 

 form B, " Vlekkanker " includes the well-known greyish-brown or purplish- 

 red or red patches in the bark first described in the canker formed on cacao and 

 subsequently in the rubber canker described by Fetch in Ceylon. Besides 

 the red canker patches of form B, the innermost layers of the bark quite near 

 the cambium, or the cambium itself, show a slight discolouration, which appears 

 on the tapping cuts in the form of diity brown or greyish points and lines or as 

 a dirty brown line in the place of the cambium. This form C gives rise to burrs 

 if not treated in time. It is not clear why Eutgers considers the two acute 

 forms, A and B noted above to be due to the same fungus Ph. Faberi. He 

 inoculated cacao PhytopJithora on Hevea and got the typical canker, form B, 

 in every case ; but when he inoculated Hevea with PhytopJithora from Hevea 

 he got the typical black vertical stripes of form A or " Streepjeskanker." 

 Sporangia weie presumably obtained from the diseased dark stripes on the 

 tapping cut where they are found in abundance in Java. It is unfortunate 

 that Hevea Phytophihora has not been inoculated on cacao, either by Fetch 

 or by Rutgers. 



According to Rutgers^ microscopic examination of sections of Hevea 

 tissues attacked by canker shows the formation of secondary cambium 

 outside the primary cambium round the brown dead cells. Mr. Bryce, Acting 

 Botanist and Mycologist to the Government of Ceylon, kindly sent me spirit 

 specimens of cankered Hevea bark from Ceylon. Sections from this bark 

 showed the formation of secondary cambium surrounding the dead cells as 

 observed by Rutgers in Java, while sections from renewing bark attacked by 

 " Black Thread " in Burma do not show any formation of secondary cambium. 

 These specimens of cankered bark from Ceylon also clearly showed the 

 microscopic differences between canker and " Black Thread." Mr. Bryce 

 also sent me specimens of diseased renewing bark from Ceylon. Not only in 

 their external characters these specimens were identical with those of " Black 

 Thread " disease of Burma, but microscopical examination also showed them 

 to be identical. At the same time specimens of " Black Thread " on Hevea 

 from Burma were sent to the Government Mycologist, Ceylon, with the request 

 to let me know if a similar disease was known in Ceylon. Mr. Bryce took the 

 trouble of examining these specimens and wrote to me that he had no hesitation 

 in pronouncing the " Black Thread " disease of Burma to be the same as the 

 one occurring on the tapping area in Ceylon where the disease is known variously 



' Rutgers, A. A. L. Hevea-Ca.n'ker^ Dep. Landbouw Nijverheid en Handel, Meded. 

 Afdeeling voor Plantenzeikten, No. 2, 1912, p. 5. 



