366 



THE AGRICULTURAL NEWS. 



November 8, 1913. 



FUNGUS NOTES. 



INFECTIOUS GUMMOSIS OF CITRUS 



TREES. 



In the A'jricuUunil Xtir.<. Vol. W, p. 20G, a summary 

 was given of a paper by (). I'.utler on (iummosis of Citrus 

 and Trunus. In this ic_ was pointed out that gummosis is 

 a condition that may arise in response to very various 

 stimuli It may be induced by fungous, insectile, physical 

 and chemical injuries, provided that they affect the cambium 

 layer at a time when growth is taking place and an abundant 

 supply of water is available. Nine fungi and certain 

 bacteria were enumerated as having been identified by 

 various workers with the malady in the two genera named. 



The results of a study of gummosis of lemon trees in 

 California are to hand in a paper by H. S. Fawcett, pub- 

 lished in the Monthly Bulletin of the State Commission of 

 Jlorticulture, for August 1913. The particular form of the 

 disease described in this paper is that which is characterized 

 by the dying of areas of bark accompanied by the exudation 

 of gum, usually somewhere on the trunk from above the bud 

 union to the forks of the branches. It may be better 

 distinguished by the name bark rot than by the general 

 terra gummosis. 



The key to the nature of the disease was obtained by 

 the discovery that it could be produced by infection of 

 healthy trees with portions of discoloured bark or wood taken 

 from the edges of a diseased area. It wan found that the 

 gum itself could not, as a rule, transmit the infection— a fact 

 which is held to account for the failure of inoculations 

 carried out by previou.s workers. Two forms of the disease 

 were distinguishable: one in which the outer layer of bark 

 was killed much in advance of the inner, and there was 

 some softening of the bark; and another in which the 

 killing of the inner bark lagged only slightly behind that 

 of the outer, and the bark remained hard as the areas 

 of infection enlarged. Both were proved to be caused by 

 fruit rot fungi familiar in California; the former by Botn/tis 

 vulgaris, and the latter by Fythiact/stis citrophthora. Inocu- 

 lations with the former showed that the lemon is affected 

 readily, the sweet orange less so, and the sour orange 

 scarcely at all. 



TRKAT.MENT. 



While the author has worked out a method of direct 

 treatment which has given promising results, he emphasizes 

 the importance of hygienic methods in preventing the 

 disea.se. The methods recommended when the disease wa.s 

 believed to be due to physiological factors have been fairly 

 successful in practice. They consist in keeping the soil away 

 from the bud unioiv, getting good drainage, using sour 

 orange stock for heavy soils, and high budded lemon trees 

 planted high for ;ill new plantings. A method of painting 

 the trees with neatsfootoil had also been adopted by growers; 

 but this has rcsult-d in damage to many trees, and is shown 

 by the author to encourage actively the growth of the Botrytis, 

 and to do nething to hinder the growth of Pythiacystis. 



The direct treatment now recommended is a simple one, 

 though obviously dependent for its success on careful 

 manipulation. By means of a farrier's knife, or a knife bent 

 sideways into half a hoop and mounted in a wooden handle, 

 the patch of dead bark is cut out, carrying the cut an inch 

 or so outside the discoloured line. Where the bark is not 

 afTected down to thf cambium only the outer dead part is 



scraped off. Where the diseased patch is too large for such 

 treatment, it is partly isolated by making a longitudinal slit 

 on each side of it. The area treated by any of these methods 

 is then painted with Bordeaux paste, for which the author 

 gives the following recipe; 



BOKDEAl'.X I".\STE. 



One pound of bluestone (copper sulphate) is dissolved 

 in 1 gallon of %ater in a wooden or earthenware vessel. 

 This can best be done by banging it in a .sack at the top of 

 the water. Two pounds of unslaked lime, slaked in about 

 igallon of water is then prepared. Stir together when cool, 

 making a light blue mixture about the consistency of white- 

 wash. If the mixture turns some other colour before being 

 apiilied, it is an indication that something is wrong. Mix 

 up fresh each day or two, as the mixed paste tends to 

 deteriorate with age. It may be applied with a large brush 

 as whitewash. 



Exudation of gum may continue for some weeks, but 

 need cause no apprehension if, at the same time, signs of 

 the formation of new healthy tissue can be detected. 



RECENT INTERESTING WORK 

 VEGETABLE PHYSIOLOGY. 



IN 



Experiments have been carried out with seeds of 

 Epilohiuin hirAutvm, which show that in water, and in the 

 dark, they germinate only very slightly, whereas under 

 otherwise the same conditions 98 to 100 per cent, germinate 

 when exposed to light. According to the Jownal of the 

 Chemical Society (June 1913), from which this information 

 is taken, the same effect as that produced by light can also 

 be attained by treatment in the dark with solutions of 

 proteoclastic ferments such as papayotin and trypsin, and by 

 low concentrations of acids (005N'. hydrochloric acid). It 

 appears, therefore, as if light acts in' mobilizing' the protein 

 of the seed. 



Another investigation of a different kind but of equal 

 interest has been the study made in Florida of the enzymes 

 in the peel of oranges with a view to ascertaining whether 

 any change takes place in their nature or activity at a point at 

 which the fruit becomes suHiciently ripe for consumption. 

 The results of this work are briefly abstracted in the .Joiirnul 

 (if tin: Chiimral Society for July 1913. The peel has been 

 found to contain peroxidase, catylase and invertase enzymes, 

 but no oxidases. During ripening, the weight of the peel 

 decreases in relation to the total weight, whilst that of the 

 juice increases about equally in this relation. The total 

 amount of acid in the juice decreases only slightly, but its 

 concentration decreases considerably, whilst the sugar 

 increases both in concentration and in total amount. 



Lastly, according to the issue of the above-mentioned 

 journal for August 1913, an investigator has been conduct- 

 ing further experiments in regard to the occurrence of 

 ure:i in plants. This substance, as is well known, is one of 

 the simplest amides, and is the chief nitrogenous constituent 

 in the liquid excreta of animals. Working with plant prepa- 

 rations obtained by ordinary expression or maceration in the 

 cold, the xanthhydrol derivative of urea was readily precipi- 

 tated. Urea has therefore been detected in Anpergillua 

 niptryPtuicil/iuiit glaiicum, carrot, potato, chicory, turnip, 

 green haricot beans, peas, lettuce, purslane, pumpkin, maize, 

 and a few others. 



