March i6, 1922] 



NATURE 



359 



Technology on material received from British North 

 Borneo and Malava. The work formed the subject 

 of an exhibit at the Rubber Exhibition of 192 1, and 

 was briefly noticed in Nature of June 16 last, p. 499. 

 It is understood that further work is in progress, 

 and that a full illustrated account of the results will 

 be published. These authors have concentrated 

 attention upon the earliest stages of the disease, and 

 obtained results which definitely advance the problem 

 a step towards solution. In transverse sections of 

 diseased bark, numerous minute golden-yellow spots 

 of irregular outline were observed in the phloem from 

 the cambium outwards. Under high magnification 

 these coloured areas sometimes appeared to resemble 

 intercellular spaces (c/. Rands's work), but on careful 

 examination the golden areas were found to be 

 sections of necrotic sieve-tubes, the waved outlines in 

 many cases being clearly transverse sections of the 

 large vertical sieve-plates characteristic of Hevea 

 phloem. In the young phloem the disease is con- 

 fined to the sieve-tubes, but in the older tissue phloem 

 parenchyma, medullary-ray cells and latex-vessels 

 have been involved in the local tissue degeneration. 

 Commonly, a diseased area was found to be more or 

 less completely surrounded by an active meristem 

 (" wound-cambium "), which in some cases gave rise 

 to lignified elements and constituted the initial stages 

 of a burr. 



It will be seen that this investigation emphasises 

 the fact that, quite apart from the latex-vessels, 

 ■elements (sieve-tubes) of vital importance in the nutri- 

 tional processes of the plant are injured during tap- 

 ping. The sieve-tubes cease to function and, in 

 becoming disorganised, initiate the condition known 

 as brown bast. The disease, therefore, is primarily 

 due to phloem necrosis analogous to the cases of 

 similar disease reported in the potato and in Liberian 

 coffee. Observations were also made regarding the 

 origin of burr development. It is stated that, as a 

 result of the activities of the wound cambiums, 

 diseased groups of cells become enclosed in " pockets " 

 of stone-cells. Sanderson and Sutcliffe also refer to 

 stone-cells derived from the pathological meristem 

 in the bark tissue. 



In reading this series of papers for the first time 

 it is difficult to believe that the authors are dealing 

 with the same problem. No evidence for a parasitic 

 origin of the disease is brought forward in any case, 

 but their respective investigations lead the authors 

 to differ in their views as to the immediate origin 

 of the disease. Sanderson and Sutcliffe point to an 

 induced meristematic activity in the bark as the 

 characteristic feature of the pathological anatomy. 

 To Rands the disease is a special case of gummosis 

 which is the outcome of a wound response resulting 

 from tapping ; while Farmer and Home regard 

 phloem necrosis as, " beyond doubt," the immediate 

 cause of the disease. The present writer carefully 

 examined Home's remarkable preparations and 

 camera-lucida drawings shown at the Rubber Exhibi- 

 tion last year, and recently he has been allowed to 

 compare further the drawings with the illustrations 

 accompanying the papers of Rands and of Sanderson 

 and Sutcliffe. He considers that the true relations 

 of the seemingly conflicting results are apparent on 

 the view that a difficult piece of anatomy has been 

 carried out to varying degrees of finality by the 

 respective workers. In the case of Home's work 

 there is little doubt that his investigation has shown 

 that the immediate cause of brown bast is a degenera- 

 tion of the sieve-tubes and neighbouring elements, 

 accompanied by the more or less complete localisation 

 of the necrotic area by an active meristem. Rands's 

 research appears to have fallen just short of complete 



NO. 2733, VOL. 109] 



success. In spite of his histological methods to prove 

 his " intercellulars " to be such, comparison of his 

 drawings with those of Home strongly suggests that 

 they are the necrotic sieve-tube areas illustrated by 

 the latter worker. It is remarkable that throughout 

 Rands's anatomical paper he uses the word " sieve- 

 tube " twice only, though in the only diagram in 

 which sieve-tubes appear each of the two sieve-tubes 

 figured is blocked with "gum." Rands's view that 

 the disease is a type of " gummosis " is by no means 

 beside the mark ; it may well be so regarded in 

 its ultimate symptoms, but he failed to detect the 

 primary cause. The abundant meristematic activity 

 emphasised by Sanderson and Sutcliffe would appear 

 to be a secondary character, and is possibly a develop- 

 ment of the pathological meristem referred to by 

 Farmer and Home. It may be significant in this 

 connection that the bark examined by Sanderson 

 and Sutcliffe was from trees which " had been taken 

 out of tapping for some little time owing to brown 

 bast," and in which, therefore, there may have been 

 time for the meristem to reach considerable develop- 

 ment. The suggestion that the pathological meristem 

 is formed as a result of the stimulus afforded by the 

 activity of the cork-cambium of the tapped bark 

 above the diseased area is interesting, and the authors 

 might usefully have given further evidence in support 

 of the contention. 



There would appear to be some difference of 

 opinion as to the condition of the starch reserves in 

 the diseased bark. Sanderson and Sutcliffe report 

 that starch is usually absent, or present in small 

 quantities only, and regard this depletion as accounted 

 for by the demands for food materials made upon the 

 neighbouring tissue by the meristematic cells. Rands, 

 however, states that evidence based on observations 

 of the starch reserves indicates that the response of 

 the tissues, resulting in the " disease," is more the 

 effect of a stimulus connected with a loss of latex 

 than of an actual depletion of (starch) reserve food, 

 though he suggests the possibility of effects caused 

 by the temporary depletion of other food substances, 

 e.g. the proteid constituents of the latex which are 

 known to suffer a reduction as the consequence of 

 hard tapping. 



If the initial occurrence of phloem necrosis is 

 confirmed, there will remain the problem of the cause 

 of this condition. The solution of the problem is 

 inseparably connected with the general question of 

 phloem necrosis in plants. Thus light may be thrown 

 on brown bast by the recent work of Quanjer, who 

 claims that phloem necrosis in the potato can be 

 transmitted from one plant to another. 



As pointed out by Farmer and Home, the current 

 investigation of brown bast disease points clearly to 

 the urgent need for a wider understanding of the 

 general physiology of Hevea, in which, of course, the 

 laticiferous system would call for special attention. 

 The present writer ventures to suggest that before 

 this question (of which little is as yet known) can 

 be dealt with successfully, it is essential that fuller 

 knowledge of the anatomy and histology of latici- 

 ferous tissue in general should be available. Useful 

 pioneer work has been done by Meunier, but the 

 papers under review show how far from complete 

 such knowledge is at present in the case of Hevea 

 alone. There is little doubt that, as in zoology, 

 comparative anatomy would be highly suggestive and 

 helpful. The study should extend at least to carefully 

 selected arboreal laticiferous plants, of which the 

 various " rubber-trees " which have been cultivated 

 or exploited commercially would probably be suffi- 

 cient, since the character of their laticiferous systems 

 varies greatly in important features. The essential 



