91 



The Supplement to the Tropical Agriculturist 



they are formed in a position where the wind 

 can easily reach them. This is not often the 

 t case, however, since spores have not been found 

 on the surface of diseased crovvus, except in 

 the comparatively small number of cases in 

 which the blade or expanded portion of the leaf, 

 is attacked. In the large majority of cases the 

 seat of attack is the compact mass of leaf bases, 

 the leaf-sheaths, which form a tubular covering 

 to the top of the stem. Having entered the 

 outermost of these, the fungus grows in towards 

 the softer underlying ones and usually does not 

 begin to produce spores until several have been 

 penetrated. Spores have never been found on 

 the hard outer sheaths, but usually occur be- 

 tween the softer inner ones at some distance 

 from the surface. Here they are not exposed 

 to the air and cannot serve as an effective means 

 of propagation. In some cases, however, the 

 young leaf shoot at the apex of the crown ia 

 found to have been attacked in the portion 

 which afterwards becomes the expanded "blade" 

 of the leaf. This usually occurs while it is still 

 small and hidden in the tube of leaf-sheaths, 

 being the result of direct contagion from the 

 latter. In a very few of these cases the parasite 

 has been found still alive when the young lf<af 

 has pushed out into the air, and it is probable 

 that, in periodsof highhumidity orduring heavy 

 dews, spores would develop in this situation, 

 freely exposed to the wind. A second con- 

 dition in which there may be air-borne 

 infection occurs when the tube of leaf- 

 sheaths begins to disintegrate as an effect 

 of the disease. In old cases the outer leaf-sheaths 

 wither and fall away and eventually nothing is 

 left but a bare pole. In these old withered 

 sheaths no spores capable of gfirmination have 

 been found, but it is quite possible that they 

 occur, and if this is so, they would be a means 

 of dissemination. A third condition is the re- 

 sult of the stripping of the outer leaves for 

 thatching and still more in some localities for 

 fibre. In the operation the old leaf bases are 

 torn away, and it is not uncommon to see leaf 

 sheaths that are still almost white from their 

 internaal position, exposed. In infected trees 

 this must offer considerable opportunities 

 for aerial dissemination of the spores. It is 

 doubtful how far the above conditions are suffi- 

 ciently frequent to account for the intensity of 

 the epidemic. It appears that if this were a 

 common method of spread, the area affected 

 would by now be far greater than it is. Airborne 

 infection is always rapid and instead of the dis- 

 ease being confined to one small district, it 

 would be found throughout the country.'' There 

 is no doubt but that the conditions mentioned 

 above do occasionally occur and that therefore 

 the wind does play a small part in disseminating 

 spores. This means of distribution is too for- 

 tuitous, however, to explain completely the 

 steady spread of the disease. 



2. Tappers.— " Dissemination of disease by 

 human agency is particularly likely where, as 

 in bud-rot, the diseased parts of the plant are 

 habitually handled by persons who afterwards 

 come into contact with susceptible portions of 

 healthy trees. As already mentioned, each vil- 

 lage uses the produce in leaves of a large uumber 

 of palmyras for thatchiDg. In addition a large 



number of trees are tapped for toddy and jag- 

 gery. Over 400,000 palms are tapped for jag- 

 gery in the Godavari district (mostly in the up- 

 land taluks) according to the Imperial Gazet- 

 teer. For both these purposes the bulk of the 

 palms in the district are climbed at intervals. It 

 is the practice of the climbers to strip off the 

 outer sheaths, both because they impede their 

 operations and because they serve for fuel. 

 Hence the inner fresh, moist and softer sheaths 

 are otten exposed. In diseased trees this is just 

 the position in which felted masses of the my- 

 celium of the parasite are found. Fragments of 

 the outer sheaths containing living mycelium no 

 doubt often break off and remain on the person 

 of the climber. The mycelium itself would 

 readily adhere to his knife. It is easy to see 

 that in repeating the operation in a healthy tree 

 there is every chance of his successfully, if un- 

 consciously, inoculating it with tho parasite. 

 There are indications in some places that the 

 disease has followed lines of communication 

 used by the people, particularly the ferries 

 across the canals which intersect the district. 

 These are 110 doubt used by the tappers and the 

 matter would be explained if the infection is 

 conveyed by them. In this district the coco- 

 nut trees are not tapped for toddy and their 

 leaves are rarely cut. Hence they are seldom 

 climbed. Arecanuts are neither tapped nor are 

 their leaves cut and when climbed it is only to 

 remove the bunches of nuts, which project 

 well away from the stem. It is possible that 

 this explains in part the comparative immunity 

 of these two species of palm." 



It is not during the process of tapping that 

 fresh palms are infected. The parts of the 

 crown that are cut to get the juice do not often 

 have the disease. It is while they are removing 

 the lower leaf-sheaths to use as fuel and to a 

 smaller extent when they do so to clear the 

 way for climbing up, that fresh palms catch 

 the disease from infective material adhering 

 to the tapper's person and instruments. This, 

 1 believe, is the chief means by which the 

 disease is spread in the delta. As it entails con- 

 siderable exertion to climb to the top of a high 

 palm, the tapper, while he is about it, removes 

 in most instances as many of the lower leat- 

 sheaths as possible and leaves exposed the 

 jiving, tender, pale, yellow leaf -sheaths within. 

 Then the palm is exposed to infection from two 

 other sources — (1) to a small extent from spores 

 carried by the wind, (2) to some extent from 

 spores and mycelium carried by insects. 



Experiments were conducted at three places 

 in the affected district in July and August 1910 

 to ascertain the method of infection. Mycelium 

 and sporangia of the lungus were cultivated in 

 as pure a condition as possible and then de- 

 posited on the surfaces of newly exposed leaf- 

 sheaths of healthy palms. 



On the 17th July the crown of a palm in 

 which the central expanding leaf had become 

 pale, was cut off in liajabhupalapatnam in the 

 morning and brought to iiamalkota in the 

 afternoon. The outer leaf-sheaths were removed 

 till clean, young spots were exposed on the 

 inner sheaths. Several of these spots were care- 

 fully cut out with a sterile knife and placed 

 on a glass stand in a moist chamber. Wex^ 



