Plant Sanitation. 



226 



[March, 1910, 



extent, but the greater part of each 

 still remains, and the wood which is 

 left is quite hard ; one of these is a 

 sapu, and the other probably Filicium 

 decipiens. 



The stump of a jak tree which was 

 felled at Peradeniya, in 1900, was dug 

 up in 1907 ; the wood was quite sound 

 except on the exterior, and though it 

 had been attacked by termites, they 

 had not been able to make much pro- 

 gress. An extreme instance was noted 

 in a case of root disease recently in- 

 vestigated ; the field was covered with 

 old stumps of " Na " (Mesua ferrea), 

 and the disease was apparently associ- 

 ated with these stumps which were 

 said to be fourteen years old. The ex- 

 terior sap wood had decayed but the 

 heart wood was quite sound, and the 

 task of cutting off a side root five 

 inches thick occupied two coolies for 

 more than an hour. Apparently these 

 stumps, though subject to a rainfall of 

 about 200 inches per year, at an ele- 

 vation of 1,500 feet, are likely to per- 

 sist for at least another fourteen years. 



I have not been able to collect further 

 data. Stumps are of course available, 

 but the date of felling and the kind of 

 tree are usually not definitely known. 

 But the evidence points to the conclu- 

 sion that on the average, under favour- 

 able conditions, "soft wood" stumps 

 may be expected to decay in from four 

 to six years, while "hard-wood" stumps 

 may persist for twenty years or more. 

 Unfortunately most of our jungle trees 

 are hard-wood trees, and two of our 

 Hevea root fungi, Fomes semitostus and 

 Sph&rosMlbe repens, usually originate 

 from a hard-wood stump, viz, Jak. 



One of the advantages which have 

 been urged in favour of open planting of 

 Hevea was conspicuously demonstrated 

 during a recent attempt to infect some 

 Peradeniya trees with " Canker." That 

 fungus spores blow everywhere has been 

 brought forward in support of the 

 erroneous theory that as far as diseases 

 are concerned thei'e can be no difference 

 between wide and close planting. But, 

 through ignorance of general mycology, 

 this objection loses sight of the fact that 

 it is not so much a question of whether 

 fungus spores will arrive at any given 

 spot as whether they will find condi- 

 tions favourable for germination when 

 they get there. The trees in question 

 form a group of thirteen planted on 

 the river-bank, in a double or triple row, 

 eight or nine feet apart ; they have been 

 referred to as affording evidence of the 

 good growth which may occur when 

 Hevea is planted at that distance, but 



the referenae is obviously misleading, 

 since only two of them are hemmed in 

 by their neighbours. An attempt was 

 made to infect these trees, on recently- 

 tapped surfaces, with bacteria and with 

 Nectria spores during the last monsoon ; 

 it was found that the stems remained 

 quite dry during the rains, owing to 

 the protection afforded by their 

 leafy crowns, and in order to imitate 

 the usual estate conditions, special 

 arrangements had to be provided to 

 keep the inoculated stems damp The 

 difference between these trees and the 

 ordinary estate trees whose stems are 

 constantly wet during the rains was 

 most marked, and was probably sufficient 

 to account for the failure of the ino- 

 culations. 



It has been suggested that if Hevea is 

 periodically defoliated by heavy rains in 

 the south-west monsoon, as stated in 

 the Tropical Agriculturist for February 

 last, the " wintering " period may ulti- 

 mately be changed from the dry season 

 to the wet season. Observations on this 

 point would be welcome, but at present 

 it appears that the "wintering" of such 

 trees takes place at the normal period, 

 so that the trees are defoliated twice in 

 the course of the year. The effect of 

 this is a diminution of the store of 

 reserve food in the tree. The new leaves 

 are constructed from the reserve 

 material of the tree, and if the tree is 

 defoliated twice, there is a double drain 

 on its stock. Professor Fitting has 

 shown that when the tapping wounds 

 are being healed, the tree draws on its 

 stock of reserve food ; from this it may 

 be deduced that the amount of food 

 which is being manufactured by the 

 leaves of the tree at any time is insuffi- 

 cient to provide for the formation of the 

 rerewed bark. It is conceivable, there- 

 fore, that the extra defoliation might 

 affect the bark renewal, but as the 

 amount of reserve food in a Hevea stem 

 is usually large, this inference is 

 probably too small to be of practical 

 importance. 



It should not be forgotten that when 

 a five-year-old Hevea tree is first tapped, 

 it has the accumulated reserve of five 

 years on which it can draw for bark 

 renewal. During the foar years' tap- 

 ping (on a four-year system) this is being 

 continually drained, and if the renewed 

 surface is immediately retapped in. the 

 fifth year, the amount of reserve food 

 then in the stem may be too small to 

 admit of rapid renewal. Professor 

 Fitting's opinion may be quoted. 

 " Whether or not it is feasible with 



