Plant Sanitation, 



138 



[August, 1909. 



lings was recently brought to notice, and 

 in this case the cause was undoubtedly 

 Pythium. But the fungus attacked the 

 top of the plant, not the base of the stem, 

 and bound together all the leaves and 

 the stem with a white film of mycelium. 

 It spread at first over the surface of the 

 leaf and the apex of the stem, and then 

 entered and killed the tissues. 



When nursery plants begin to die 

 off in patches, all the dying plants must 

 be removed and burnt at once. If their 

 death is not due to eel worms, the bare 

 patches should be watered with one per 

 cent, solution of formalin, i.e., one part 

 of commercial formalin in forty parts of 

 water ; or they should receive a liberal 

 dressing of slaked lime. In the " damp- 

 ing off" of coniferous seedlings, it has 

 been found that the disease was to a 

 great extent prevented by disinfecting 

 the beds with a one per cent, solution of 

 formalin five days before sowing the 

 seed ; and further, that it could also be 



Erevented by sprinkling clean sand, as 

 ot as it could be handled, over the beds 

 to a depth of about one-sixteenth of an 

 inch immediately after the germination 

 of the seed. It is obvious that when 

 nurseries are attacked by any fungus 

 disease, all shade should be removed as 

 far as is possible without injuring the 

 plants. 



In the last number of the Tropical 

 Agriculturist, it was stated that the 

 death of the bark of Hevea, or at least 

 its sepaiatiou from the wood, must 

 precede the accumulation of rubber be- 

 tween the wood and the bark. Since that 

 was written, I have received, per the 

 Editor of the Times and Mr, 0. North- 

 way, two specimens showing these rub- 

 ber pads ; they were described by Mr. 

 North way in the local papers on June 

 8th. Each specimen consists of a strip 

 of bark, 10 centimetres broad {i.e., hori- 

 zontally round the tree), and 6 centime- 

 tres high. The thickness of the bark, 

 after several days' drying in transit, is 

 three to four millimetres {i-e., three- 

 twenty-fifths of an inch); it would be 

 thicker when fresh. The trees had been 

 scraped some considerable time before 

 pricking, since each piece shows a well- 

 developed outer brown layer, one-fiftieth 

 of an inch thick, scaling off, and a fur- 

 ther thickness of one-twenty-fifth of an 

 inch turning brown ; so that half the total 

 thickness of the bark is already cor- 

 king off as a consequence of the scraping. 

 This uniform scaling off has nothing to do 

 with the formation of the rubber pads. 

 Specimen A has, in the middle, a patch 

 of dead bark {i.e., dead right through 

 to the cambium) about 5 centimetres 

 in diameter, with a pad of rubber of the 



same size behind it ; it forms a blister 

 raised about 6 millimetres above the 

 surrounding level ; there are two lines of 

 pricker cuts across the specimen ; one of 

 these just touches the edge of the rubber 

 pad. The other passes over the pad at 

 a distance of one centimetre from its 

 edge ; the outer surface of the pad is 

 marked with the incisions of the pricker, 

 and fragments of bark have been pushed 

 into it, while the inner surface bears 

 corresponding projecting teeth of rubber 

 which have beeu pushed out by the 

 pricker ; the pieces of bark within the 

 pad and the marks of the pricker on both 

 surfaces prove conclusively that the pad 

 was formed before the bark was pricked. 

 Specimen B is similar ; the blister in this 

 case measures 8 centimetres by 5 centi- 

 metres, and the rubber pad is one centi- 

 metre thick ; there are three lines of 

 pricker cuts, of which the upper and 

 lower just touch the edges of the pad, 

 while the middle line goes right across 

 it, but, in consequence of its thickness, 

 the pricker cuts do not penetrate com- 

 pletely through it ; as before, the dead 

 bark has been driven by the pricker into 

 the pad, and this shows that the pad 

 was formed before the bark was pricked. 

 The bark round the blister, which was 

 living when pricked, shows only the 

 usual pricker cuts through it. In speci- 

 men B, a new bark is growing under 

 the edge of the pad at one side, and as 

 this new bark is 6 millimetres broad, the 

 pad must have been in existence for 

 some time. 



Further light is thrown on this pheno- 

 menon by another specimen which has 

 been 9ent in, showing the death of the 

 bark in patches after scraping. In thi9 

 case it was detected at once, and there 

 had been no time for its separation from 

 the wood and the consequent formation 

 of a rubber pad. Normal Hevea bark is 

 protected from injury by its outer brown 

 dead layer. When this layer is scraped 

 off, the inner tender living tissues are 

 exposed and they immediately begin to 

 die back. As a rule they die back uni- 

 formly and form another continuous 

 outer brown layer, but in some cases, a 

 patch of bark two or three iuches in 

 diameter dies right down to the cam- 

 bium. When this dead patch splits 

 away from the wood, rubber pads are 

 formed by the inflow of latex from the 

 surrounding healthy bark. There seems 

 to be no explanation, other than expo- 

 sure to sunlight, etc., for the production 

 of these patches of dead bark. I have 

 not been able to find any fungus in them, 

 though there is a well-known semi-para- 

 sitic fungus of Hevea which might be 

 expected to produce such a result. The 

 fact that the dead bark is strictly 



