Timbers. 



[November, 1910. 



If the purchaser wishes he may leave 

 the selection of the samples to the 

 Bureau of Forestry- simply statiug, for 

 example, that he wishes samples of the 

 woods he is apt to run across in such 

 and such a province or for such and such 



a purpose, as for furniture-making ; or, if 

 he hesitates as to how much money to 

 send in such cases, he may write to the 

 Director of Forestry for a suggested list 

 of samples, and from these he can select 

 his own order. 



PLANT SANITATION. 



MISCELLANEA : CHIEFLY 

 PATHOLOGICAL. 



By T, Petch, b.a., b.sc. 



One of the most important discoveries 

 made by Professor Fitting in his in- 

 vestigation into the effect of tapping on 

 Hevea was the fact that the bark which 

 is renewed beneath the pricker cuts con- 

 tains an abnormal number of " stone 

 cells." Beneath each incision made by 

 the pricker, a group of stone cells is 

 formed, instead of the normal laticiferous 

 tissue, and therefore the renewed bark 

 after pricking contains less latex than 

 normal bark. But he pointed out that 

 further investigation was required to 

 decide how long this formation was 

 continued. 



Examination of a piece of pricked 

 bark, six months after pricking, shows 

 that the stone cells are still in contact 

 with the cambium, though it is evident 

 from their shape that the excessive for- 

 mation is about to cease. This particular 

 piece of bark had been pricked but not 

 pared, and therefore it should show the 

 effect of the pricker to the fullest 

 extent, because the formation of new 

 bark is less after pricking only than 

 after pricking and paring. 



A second sample of bark was taken 

 from a tree that had been pricked and 

 pared, about twelve months after the 

 operation. The thickness of the renewed 

 bark was 4 mm. at the point beneath 

 the pricker mark, and the abnormal 

 group of stone cells extended from the 

 exterior to a distance of 1*75 mm. 

 from the cambium. Seven-sixteenths, or 

 nearly one half, of the renewed bark 

 was of normal structure, and it would 

 therefore appear that the formation of 

 abnormal stone cells ceased about six 

 months after pricking. In all pro- 

 bability it ceased earlier than this, for, 

 as the following example indicates, the 

 bark does not increase in thickness at a 

 uniform rate. The increase is greatest 

 immediately after tapping ; afterwards 

 it slows down until it ultimately approxi- 

 mates to that of the untapped bark. 



A third sample was taken from a tree 

 which had been similarly pricked and 

 pared, three years after the operation. 

 The thickness of the renewed bark was 

 5£ mm., and the groups of stone cells 

 extended to a depth of 2\ mm. from the 

 cambium. Here again nearly half the 

 bark was of normal structure. 



It should be pointed out that isolated 

 stone cells occur throughout the bark of 

 Hevea. These may be distinguished from 

 those due to the pricker by the fact that 

 their long axes are, as a rule, parallel to 

 the cambium, while the latter have their 

 long axes usually perpendicular to the 

 cambium. 



It may be concluded from the above 

 that the effect of the pricker on the 

 cambium passes off after about six 

 months, but the groups of stone cells 

 persist in the outer half of the bark 

 after three years from pricking. As the 

 greater part, or almost the whole of the 

 latex, is obtained from the inner two 

 millimetres of the bark, they will not 

 have much effect on the flow of latex 

 after three years. 



It must be mentioned that the measure- 

 ments given above were made on bark 

 preserved in alcohol, and that the outer 

 dry brown bark is not included. 



On reading the descriptions of Hevea 

 diseases, .one frequently finds that the 

 exudation of latex from the stem is 

 regarded as a characteristic symptom. 

 For example, it has been described as 

 the first symptom of " dieback," and one 

 of the characters of " pink disease." I 

 have made careful observations on this 

 point, and have never been able to find 

 that the exudation of latex can be taken 

 as a sign of disease. Indeed, all the avail- 

 able evidence yoes to show that diseased 

 bark cannot yield latex. When trees 

 are attacked by "canker" or "pink 

 disease," the latex in the piece of bark 

 attacked is coagulated in the latex tubes, 

 and it cannot run out. 



That coagulated rubber may be found 

 on bark attacked by Corticium javani- 

 cum or " canker " is undeniable, but its 

 presence there is a secondary symp- 

 tom and it does not occur until the 



