Plant Sanitation. 



556 



[December, 1908. 



districts in the Islands. A Secretary 

 of Nagcarlan, now dead, noticed the 

 restricted occurrence of the disease long 

 since, and from it deduced the mistaken 

 theory that the disease was caused by 

 cold. The coconuts at the foot of Mount 

 San Christobal, which are comparatively 

 unreached by the wet ocean winds, are 

 free from bud rot. The people of Lilio 

 and Nagcarlan maintain that the disease 

 is gradually descending into the lower 

 groves. Below the zone where the bud 

 rot is most at home, there is of course 

 a region in which infection can occur 

 under conditions^temporarily favourable, 

 or affecting single trees or small loca- 

 lities. As any tree for miles around is 

 likely to receive the germs, it is inevi- 

 table that in this lower zone some will be 

 infected each year. As these die, the 

 damage is cumulative, and the gaps in 

 the lower groves increase in number or 

 size. But I can see no good evidence 

 that the region in grave peril is widen- 

 ing downward. As already stated, there 

 are spots, probably even as low down as 

 Fagsauitan, where single or few trees 

 have succumbed ; but even higher up 

 than the centres of population of Nag- 

 carlan and Lilio the climatic conditions 

 have prevented these spots from becom- 

 ing centres for the rapid spread of the 

 disease. 



Further evidence that humidity is a 

 condition of contagion is found in the 

 fact that young trees are more suscep- 

 tible than old ones. About the crowns 

 of old tall trees the air moves compara- 

 tively freely, and keeps them compara- 

 tively dry. Every inhabitant of the 

 infested district recognizes the greater 

 susceptibility of the young trees ; the 

 general opinion is that for every old 

 tree killed, two which are just coming 

 into fruit, or would do so within a year 

 or so, die, although the total number of 

 such trees is naturally much less than 

 that of adults. On the other hand, very 

 young trees, of two years or less, are 

 for some reason comparatively rarely 

 attacked. 



Since humidity is the condition of 

 easy infection, the extension of the 

 disease occurs principally during the 

 most humid season. At the present 

 time there are numerous trees in 

 advanced stages of the disease, but ex- 

 ceedingly few which show the first 

 symptoms. 



The first symptom always in young 

 trees, and almost always in old trees, 

 is the yellowing and wilting of the 

 youngest, still folded leaf. The disease 

 attacks the soft, undifferentiated tissue 

 of growing points. It is likely that 

 infection normally occurs where the 



germs can get direct access to these 

 points without penetrating through 

 mature tissue, but the germs might also 

 be borne by insects which could carry 

 them through mechanical lesions in old 

 tissue. In young trees, the youngest 

 leaf presents the only possible path of 

 direct unaided infection ; and however 

 infection might occur the youngest leaf 

 is directly inserted in the tissue suscep- 

 tible to rot, and must die before the 

 rot embraces most of the soft tissue 

 — commonly known in English as the 

 "cabbage." As soon as the youngest 

 leaf is noticeably discolored it can easily 

 be drawn out. The next youngest 

 leaves follow in rapid succession. With- 

 in two or four months after the disease 

 can first be detected most of the 

 leaves will have fallen. A few of the 

 oldest leaves grow from tissue so hard 

 that the rot makes little or no progress 

 in it; these leaves, four to a dozen in 

 number, persist for months after the 

 younger leaves are gone. It is in this 

 stage, with a thin whorl of old leaves 

 crowning the stem, that most of 

 the diseased trees are found, at least 

 at this season. These leaves very likely 

 fall only when their natural time comes, 

 uninfluenced by the rot. 



In the case of old trees, the young 

 flowering branches, like the youngest 

 leaves, spring from near the soft heart. 

 Infection might occur along these 

 branches, and they might give the first 

 external signs of disease. In some coun- 

 tries the withering or fall of these 

 branches is said to be the first symptom 

 of bud rot, and some of my informants 

 state that this is sometimes the case 

 here. No such case came under my 

 notice, but, as already said, there are 

 now very few trees showing any early 

 symptoms. Branches whose nuts are 

 more than half grown are grounded in 

 mature enough tissue so that the disease 

 does not usually prevent the nuts from 

 maturing. But no new nuts are set 

 after the appearance of the rot, and 

 the youngest nuts almost always, or 

 quite always, fall without becoming ripe. 



As has been found always true _ of 

 coconut bud rot elsewhere, the decaying 

 tissue has a powerful and vile odour. 

 The stench is very characteristic but 

 not easily described ; one of its com- 

 ponents is the smell of tan. An attempt 

 is now being made in the Government 

 Laboratory to separate the organisms 

 present, and this will be followed by 

 inoculation experiments. I have already 

 ascertained that no fungus mycelium 

 is present in the advancing border of 

 the diseased tissue. 



The inhabitants of Ylaya have found 

 that if the first leaves affected are pulled 



