294 



Thirdly. It cannot attack healthy uninjured buds, but is in fact 

 a wound parasite only. It can attack young imperfectly developed 

 leaves. 



Fourthly. In such attacks as on a leaf or wounded bud the plant 

 defends itself from further injury by throwing off the infected dead 

 portion, whether infected leaves or internode. This indeed is one of 

 the great defences of the Para rubber tree, its deciduousness, and it 

 is from this power of shedding its leaves and their actual short life, 

 that the leaf-fungi Pestalopjzia etc., do it so little harm. Before 

 the fungus has been able to spread over the leaves of the tree so as 

 to cause a serious injury to the foliage, the tree sheds its leaves. 

 Many of the spores must be lost on the ground, and the infection of 

 adjoining leaves is naturally slower. Compare with this the infection 

 of long lived nondeciduous leaves, such as Coffee with Hemileia or 

 Cloves with Cephaleuros. Each leaf is infected at several different 

 spots and the spread of the fungus, or in the second case the Alga, 

 is much larger and more continuous. The life of the Hevea fungus 

 is practically shortened with the short life of the leaf, and often it has 

 apparently hardly time to produce spores before the leaf falls. 



In Borneo a lot of sixty trees together were attacked and killed 

 besides isolated trees here and there in the plantations. It does not 

 seem likely that all of these sixty were wounded, unless by topping, 

 so that it is possible that it may be able to attack at a weak point, 

 such as the young leaves as seen in Experiment E. 



Much probably depends on the power of the plant to cut off the 

 infected dead portion as in the case of the leaf stalk in F. and in the 

 cases where after destruction of the bud the next internodes died and 

 were isolated by a growth below the dead portion. This would not 

 be possible in a thick stem of a two year old tree, as the shoot would 

 be too thick. 



It must be noticed that the length of the life cycle in the case of 

 the petiole in F. was very short, especially when compared with that 

 of the trunk of the tree sent from Borneo. The latter had been sent 

 from a considerable distance to Singapore and remained for a week 

 in the office before it produced spores. The upper part of this tree 

 must have been diseased for a long time before it was sent as the 

 cambium was destroyed for nearly its whole length. Possibly the 

 development of the fruit requires the complete death of the portion 

 attacked, or its almost complete deprivation of water, which would 

 naturally take longer in the case of a thick stem than in a slender 

 leaf stalk, which indeed had become detached before the spores were 

 matured, or it might depend on the humidity of the air, for as has 

 been mentioned, the fall of a heavy shower of rain after a long di7 

 spell on the night of May l6 was followed immediately by develop- 

 ment of spores. The rain ceased about 7 a.m. and the stems were 

 seen to be covered with masses of spores about 8 a.m. There were 

 none on the previous evening. In the case of the young leaf and 



