55 



in one or two it was said that the disease had been checked for a 

 time and had then re-commenced. 



The whole of the stem and root system is perfectly healthy up 

 to a late stage in the disease. With the crown, however the case 

 is otherwise. The expanded parts of the leaves are, it is true, 

 unaltered and apparently healthy until withering sets in. In the 

 leaf sheaths, however, the signs of disease are unmistakeable. 

 These sheaths are a remarkable feature of the structure of most 

 palms. They form a series of twenty or thirty tube-like layers 

 closely applied one under another so as to form a funnel. The 

 actual top of the stem or apical bud is sunk in the centre of this 

 funnel and protected by it, a protection which is a necessary one, 

 for it is the most vulnerable part of the tree and death follows its 

 destruction. To reach the apical bud a parasite must penetrate 

 these layers. This is what actually happens. 



The leaf sheaths of all diseased trees are marked by irregular, 

 sunken spots in greater or less number. In the earlier stages, and 

 particularly in the inner layers where young ones are often nume- 

 rous, the spots are white ; later on they become brown. They are 

 always sunken and usually have somewhat raised edges. They 

 begin on the outer sheaths and may be traced in through succeed- 

 ing ones towards the heart of the bud. As the inner layers are 

 softer, the inside patches are often larger than those outside, and 

 may even give rise to new patches which extend out again to the 

 outside sheath. In all cases, however, the first appearance is on 

 the outer sheaths. The earlier patches are dry and either free 

 from any appearance of a parasite on the surface or covered with 

 a white mycelial felt. Very soon a wet rot follows, which extends 

 with great rapidity in the delicate central tissues and converts the 

 whole heart into a foul smelling mass of putrefaction, in whichevery- 

 thing is involved, and the original agent is lost sight of. It is at 

 this stage that the insect grubs referred to make their appearance, 

 possibly attracted by the smell. They are, however, of several differ- 

 ent kinds, often absent altogether, and evidently not connected 

 with the disease. 



It is only in the early stages before the wet rot starts that the 

 true cause can be made out. This is a fungus of the genus Pythium, 

 a near ally of the Phytophthora found in" koleroga." In quite young 

 spots the mycelium is found only within the leaf tissues, where its 

 threads extend between the cells sending little branches or hausto- 

 ria into them. These are the feeding organs of the fungus by means 

 of which it absorbs the living cell substance and kills the cells. 

 Later on it comes out on the surface, forming often a dense white 

 felt or filaments bearing sporangia. The fungus resembles that 

 found in " kole roga." It is, however, formed of larger threads 

 and has a different manner of germination of the sporangia. In- 

 stead of the zoospores escaping directly from the sporangium 

 after it falls into the water, they come out in an immature condition 

 into a thin bladder formed at its top and finish their development 

 here. Then they escape and swim off in every direction. After 



