358 



NA TURE 



[March i6, 1922 



vestigations throw much light on the anatomy of the 

 diseased tissue and the probable immediate cause of 

 brown bast, while in the case last mentioned it seems 

 probable that a valuable advance has been made 

 towards a correct understanding of the nature of the 

 disease. 



The two papers of Rands (i) and (2), who pub- 

 lished preUminary reports in 19 19 and 1920, are 

 complementary. The first-mentioned paper contains 

 a full statement to date of the results of the author's 

 investigations commenced in 191 8 at the instance 

 of the Director of the Government Rubber Estates 

 in the Dutch East Indies, and still in progress. 

 Rands's results support the view of the non-parasitic 

 origin of the disease, and indicate that the repeated 

 withdrawal of the latex from the same tissues is 

 the chief causal factor concerned. The drained 

 tissues, respond by secreting a gum, which in its 

 effects prevents a further loss of latex. The time- 

 interval between successive tappings and the system 

 of tapping adopted appear to be the most important 

 predisposing factors ; in the author's experience 

 a heavy occurrence of the disease is invariably 

 associated with a drastic system of tapping. The 

 second paper records the botanical (anatomical) evi- 

 dence on which the results are based. According to 

 Rands, brown bast appears to be a special type of 

 wound-gum secretion favoured by conditions which 

 promote the vital activity of the tree. The character- 

 istic brown discoloration of the diseased bark is stated 

 to be due to the deposition of a yellow plastic " gum " 

 in the cavities of the latex- vessels and in many of the 

 intercellular spaces of the bark (phloem) parenchyma, 

 thus recalling similar observations made by Bobiliofi. 



The gum is formed, not by the breaking down 

 of cell-walls, but as a secretion of the protoplasts 

 of the parenchymatous cells adjacent to the latex- 

 vessels. It passes into the latter through the common 

 cell- wall (which is thereby stained yellow), and also 

 into the existing intercellular spaces or into such 

 spaces formed and enlarged under the stimulus of 

 the secretion. It is secreted in largest quantities 

 during the wet season, and is most abundant in 

 vigorous trees in full growth. Investigation showed 

 that the gum is practically identical with the " wound- 

 gum " formed locally as a result of artificial wounds 

 made in the wood and bark of the tree, and is similar 

 to the corresponding product in other plants. It 

 differs from the true gums, however, in its chemical 

 reactions. The clogging of the latex-vessels appears 

 to be the chief factor in arresting the latex flow, 

 but the coagulation of the latex within the vessels is 

 also indicated as a contributory factor. Under the 

 highest powers the gum is seen to possess a well- 

 marked alveolar structure which is not an artefact. 

 Rands was unable to determine whether the gum- 

 formation results from enzyme action, as has been 

 suggested in the case of the gummosis of Prunus. 

 As regards the burrs, Rands's results in general con- 

 firm the previous work of Rutgers, Bateson, Bryce, 

 and others, and especially the suggestion of Bateson 

 that burr-formation is favoured by excessive tapping. 

 The woody burrs arise from the activity of a second- 

 ary cambium formed about a group of gummed 

 latex- vessels ; the varied form of the mature structure 

 (pea-shaped, knobby, or plate-like) depends upon the 

 disposition and extent of the secondary cambium. 



The book by Sanderson and Sutcliffe (3) is primarily 

 intended as a practical guide for estate managers in 

 diagnosing the disease and in treating affected trees. 

 The authors lay special emphasis upon the desirability 

 of early treatment, and recommend " stripping " of 

 the bark, not only as curative in effect, but also as the 

 simplest and cheapest procedure. A considerable 

 portion of the book, however, is devoted to the results 



NO. 2733, VOL. 109] 



of a microscopical study of the disease, and the 

 authors claim their work to be the first attempt to 

 describe the pathological anatomy of brown bast and 

 to formulate a theory by which the observed facts 

 may be explained. They regard brown bast as physio- 

 logical in origin, and consider tapping to be its prime 

 cause. As regards pathological anatomy, Sanderson 

 and Sutcliffe find that the constant and characteristic 

 feature is a meristematic activity of the parenchyma 

 cells of the bark. Other characters described by them, 

 viz. the deposition of " tannins " and crystals of 

 calcium oxalate, the occurrence of abnormal numbers 

 of stone-cells at unusual depths in the bark, the deple- 

 tion of starch, and the presence of globules of " oil or 

 fatty matter " (suggested possibly as a substitution 

 product for starch, or as the result of a breaking 

 down of that substance), are regarded as secondary 

 symptoms arising from the meristematic activity. 



Elsewhere, however, the authors state that the 

 occurrence of " tannins " is not characteristic of the 

 disease, while large numbers of oily globules are not 

 constantly present. The meristematic tissue origin- 

 ates at a point roughly corresponding to the depth of 

 tapping, and occurs almost invariably in the imme- 

 diate vicinity of the latex-vessels. The result is a 

 partial displacement of these vessels, which, in con- 

 sequence, are often ruptured, the latex percolating 

 into the intercellular spaces, where it coagulates. The 

 latex within the vessels also appears to be coagulated 

 in situ {cf. Rands), possibly through the agency of 

 the by-products of the metabolism of the actively 

 dividing cells. The coagulated latex is considered to 

 be an additional source of irritation, stimulating the 

 surrounding tissue to further meristematic activity. 



The views put forward by these authors as to the 

 immediate origin of the disease are interesting. They 

 consider that the abnormal meristem may be due to 

 the stimulus arising from the wound meristem formed 

 just beneath the surface of the tapping cut, or it may 

 be a secondary effect of the abnormal vigour of the 

 cork cambium which early arises over the previously 

 tapped surface to form the renewal bark. Sanderson 

 and Sutcliffe regard it as " highly probable " that the 

 growth of this cork cambium " provides the stimulus 

 for starting meristematic activity at an equal, or 

 almost equal, depth in the cortex below the tapping 

 cut, i.e. in the untapped portion of the cortex below." 

 Such induced cambial activity spreading from the 

 renewal bark was first described by Lock, but it is 

 not quite clear from the present paper whether 

 Sanderson and Sutcliffe have independent evidence of 

 a similar phenomenon in the case of brown bast. 



As regards burr-formation, the case is put that, 

 while the meristem of brown bast may remain as 

 such, it may also give rise to woody tissue internally 

 and unlignified elements externally. It is in this 

 latter manner that burrs originate, and the degree 

 and character of the burr-formation depend upon the 

 amount and disposition of the meristem concerned. 

 Sanderson and Sutcliffe ascribe considerable import- 

 ance to the production of stone-cell tissue as a second- 

 ary character of brown bast. In this respect they 

 are supported by other writers. The cells on the 

 outer limits of the meristem may be largely converted 

 into stone-cells, which sometimes form extensive 

 scleritic masses resulting in the scaling of the outer 

 bark. The observations of Gandrup (4) are interest- 

 ing in this connection, since this worker shows that 

 in the young Hevea plant the stone-cells arise among 

 the thickened prosenchymatous pericycle fibres (bast 

 fibres), which later are almost completely replaced by 

 a ring of stone-cells. 



The papers of Farmer and Home (5) and (6) give 

 the results of a research carried out in the botanical 

 laboratories of the Imperial College of Science and 



