Volume 10

Scientific memoirs by medical officers of the army of India.

Date:
1885-1901
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Scientific memoirs by medical officers of the army of India. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    147/178 (page 127)
    VIII—Uredinous blight affecting the leaves of the Teak (Tectona grandis). This disease is excessively prevalent among Teak trees in the neighbour, hood of Calcutta, and is probably one reason of the relatively poor growth which they make within the locality. It makes its appearance regularly in the course of the autumn and shortly becomes excessively prevalent, being in fact one of the principal causes which lead to the leaves assuming the very unsightly, tattered appearance which they constantly present during many months of the latter part of their existence. The under-surfaces of the affected leaves become gradually covered by large patches of a brilliant yellow colour, and presently afterwards the tissues of the entire thickness of the lamina in corresponding areas dry up and become brown and so brittle that they readily break away and leave ragged irregular holes in their place. The orange discoloration not infrequently covers the greater part of the entire under-surfaces of the leaves, and, once it has begun to appear, spreads with wonderful rapidity. On examining the leaves more closely the orange discoloration is seen to be dependent on the presence of a dry, pulverulent material which first makes its appearance in isolated points, but soon becomes diffused and continuous, owing to the confluence of the latter with one another. When examined microscopi- cally, this powder resolves itself into a mass of innumerable orange spores of characteristically uredinous appearance (Plate VI, Fig. 9). They are broadly oval, or, in many cases, almost spherical in form, giving average diameters of 24 X 21u, and are provided with a conspicuously and coarsely tuberculate epispore. The presence of germinal pores is hard to recognise, save in the case of spores which have germinated, but in these, under the in- fluence of staining reagents, a varying but always considerable number of them may be detected, distributed irregularly over the surface. They germinate rapidly and freely when ripe, in distilled water, giving origin to germinal tubes, which, with- in the course of twenty-four hours, have assumed the character of very long, sinuous, occasionally branched filaments, the apices of which are occupied by dense masses of colourless protoplasm and accumulations of orange, oil matter. The mere presence of moisture is thus all that is necessary to induce the contents of the spores to travel over very considerable distances in quest of a suitable nidus for farther development. As a rule, only a single tube emerges from each spore and, as the protoplasm and oil advance along the course of it, the parent spore and the proximal portion of the tube are gradually com- pletely emptied. Mere immersion in water does not obscure the tuberculation of the epispore as it does in the case of many other kinds of uredospores, and