62 



THE AGRICULTURAL NEWS. 



February 15, 1913. 



FUNGUS NOTES. 



INOCULATION EXPERIMENTS WITH 



COTTON BOLL ROTS. 



The following extract, taken from the E.i'peri- 

 inent Station Record, Vol. XXVII, No. 8, contains the 

 results of recent work by Edgerton on the mode of 

 infection of CoUetotrichum gossypii which is the 

 cause of anthracnose, and of Bacterium maliacearuvi 

 which induces boll rot, in the cotton plant: — 



The studies of Barre relating to flower infection by the 

 fungus causing cotton anthracnose led the author to investi- 

 gate the subject at some length. He claims that infection of 

 cotton bolls following flower inoculation can take place in 

 either of two ways. The system may grow saprophytically 

 upon the dead flower parts and finally grow through and into 

 the boll, or it may cause the disease by growing down through 

 the pistil into the boll. The anthracnose probably follows 

 both methods, while the cotton bacterium {Bacterium malvn- 

 cearum) infects the bolls through the first method. 



The author carried on a large number of inoculations in 

 which he injected organisms suspended in water into the 

 flowers, and determined the infection. More than half of the 

 diseased bolls were attacked at the tip, while the percentage 

 of infection along the line.s of dehiscence was small. When 

 the bolls are small they are readily infected, with anthracnose, 

 though, so far as the observations of the author go, no one 

 part of the boll is more susceptible than another. It is 

 evident that the bolls may be infected through the flowers, 

 but the author claims that this is not the usual method of 

 infection. 



PEA DISEASE OF RUBBER TREES. 



A peculiar pathological condition of the stems of rubber 

 trees is described in the India Ruhher Journal, for Decem- 

 ber 7, 1912, where it is stated to occur in Java on Hcvea 

 and Ceara. The popular name for the ailment is 'pea 

 disease" — a name employed to describe the pea-like structures 

 characteristic of the disease. Unlike the knot of citrus trees, 

 plant galls and similar morbid outgrowths, these pea-like 

 .swellings on the bark of rubber trees do not appear to be 

 infectious: that is to saj-, no parasitic organism has been 

 found associated with them, and therefore they must be con- 

 .sidered as originating from some physiological disturbance. 



It is fairly well known that trees which have been 

 tapped badly, or in which the cambium has been penetrated 

 during tapping operations, develop uneven surfaces. In 

 some cases where the wood has been exposed, large 

 protuberances occur, which may render tapping quite im- 

 possible for many months, and even for years. The burrs of 

 the pea disesise, however, arise in a more insidious way. and 

 the remarkal)le feature of these structures is that many of 

 them occur where there is no trace of any wound having lieen 

 inflicted, or any fungus or insect having attacked the bark 



Each burr is quite woody in structure, is completely 

 surrounded by cortex and — what is very typical — each of 

 these little structures possesses a cambium of its own, and 

 can therefore produce new wood until it becomes quite 

 a large body. In other words each burr would appear to be 

 a kind of adventitious woody bud. 



The occurrence of these structures is said to cause 

 a considerable amount of damage to the trees on which they 

 grow. Tapping is interfered with owing to their .spread and 



fusion, and the secretion of latex in their vicinity is con- 

 siderably reduced. L'ea disease also induces cracking of the 

 bark. Damage of tlys nature is of sufficient importance to 

 warrant prompt attention. 



At present, the only remedy lies in removing the small 

 burrs with a penknife. It should be borne in mind that 

 careless tapping encourages these growths, any wounding of 

 the cambium being almost certain to induce the condition. 



Pea disease has been recorded on the bark of apple and 

 pear trees in America and in Great Britain, as well as on 

 rubber in the Tropics. It probably occurs in the West Indies. 

 Any local observations on the subject, together with specimens, 

 would be gladly received at the Head Ottice of this Depart- 

 ment. 



THE TAPPING OP RUBBER TREES. 



The India Rubber ^Vorld. for January 1, 191:i, 

 thus abstracts a paper by R. Fyfte on this subject, read 

 at the recent Rubber Conferenr-e in Xew York, held 

 in connexion with the Third International Rubber 

 Exhibition: — 



The operation called tapping is one of extreme impor- 

 tance and the presetjt methods are susceptible of marked 

 improvement. This subject did not receive the consideration 

 in the London Conference of 1911 that its importance 

 warrants. 



After the close .of that exposition the author toured 

 through Ceylon, the Federated Malay States and Java, study- 

 ing the preparation of rubber and methods of tapping. 

 Subsequently, he raa<le many tapping experiments atad reached 

 the conclusion that the best method was a combination of 

 excision and incision. 



Excision alone he believes detrimental to the tree, as 

 the coolies in their endeavour to get the maximum latex 

 almost inevitably cut too <leep, thus injuring the lactiferous 

 tubes close to the cambium These deep wounds heal slowly, 

 retard the growth of the tree and give access to fungus. He 

 does not consider incision alone practical, but advocates 

 a shallow excision combined with incision made by a fine 

 push pricker. Where the points of the pricker are fine they 

 may penetrate the cambium without injury. He does not 

 advocate broad blunt teeth. He got satisfactory results from 

 a push pricker with gramaphoce needles filed flat on two sides 

 and fitted i- inch apart into a small block of wood. He 

 followed the half herring-bone .system on about one-third of 

 the tree's circumference. 



Energy for Carbon Assimilation.— From the 



recent mea>uremonts of Brown and Escombe (Proceedings of 

 the Roi/al Soriiii/, 1905, "(i B) of the actual enerey 

 absorbed by the green leaf during the period of assimil- 

 ation, it appears that under the most favourable condi- 

 tions nearly 100 per cent, of the total light energy absorbed 

 is utilized in bringing about chemical change. The leaf 

 seems, in fact, to be an almost perfect photochemical midline; 

 moreover, the photochemical change produced in the leaf 

 ditters from all others, not only as regards the enormous 

 amount of energy actually absorbed, but in the fact that this 

 energy is mainly taken up from a portion of the spectrum, 

 which is usually inactive photochemically: in other words, 

 chlorophyll has properties which distinguish it from most 

 other colouring matters. (From a paper in Science Progress, 

 October 1912.) 



