October, 1910.] 



313 



Plant Sanitation. 



first is grey as if dusted with white 

 powder but when mature it becomes 

 pure white. The lower surface produces 

 colourless spores which, with the out- 

 growth of fungus filaments, give the 

 white appearance to the under side of 

 the blister and on some vigorously grow- 

 ing blisters slightly to the upper side 

 also. In not a few cases the form of 

 blister is reversed and both forms may 

 be found on the same leaf ; but the spore- 

 bearing surface is always principally on 

 the under side cf the leaf. After a time 

 the white blister becomes discoloured 

 till it is dark brown or black, then it 

 becomes dry and shrinks till the dis- 

 coloured patch is in the same plane as 

 the rest of the leaf. 



After the leaves of a bush have been 

 attacked the disease spreads to the leaf 

 stalks and the young, succulent, green 

 stems, but here the appearance of the 

 disease is not so conspicuous though the 

 damage is much more serious. The 

 course of the disease on the young deli- 

 cate stem is like that on the leaf, only 

 no blister is formed. The colour of the 

 spot is very similar, but the deep red 

 tinge is wanting. The spot becomes 

 elongated and also gradually spreads 

 round the stem. At this place the stem 

 becomes slightly swollen. When the 

 spores are ripe they give a grey appear- 

 ance to the spot but it does not become 

 pure white like the blister. The disease 

 eats through and the leaves and buds on 

 the green stem above wither and blacken 

 while the stem bends over and falls off 

 at the diseased part. Several of these 

 dead twigs on a bush give it a black, 

 unsightly appearance. 



When a thin section of a blister is 

 looked at under the microscope fine 

 colourless threads (hyphse) of the fungus 

 are seen between the cells of the leaf, 

 These come to the surface on the white 

 side of the blister and produce spores at 

 their ends. There are two kinds of 

 spores. The first is two-celled and is 

 produced at the end of a long stalk. The 

 second kind is one-celled and is produced 

 on a very short, thin, stalk from the 

 swollen end of a hypha. In the latter 

 case spores are always produced in pairs. 



When kept in a moist chamber on a 

 slip of glass or on the surface of a fresh 

 tea leaf the spores swell slightly and 

 germinate within 5£ hours of being sown. 

 From each of the cells of a two-celled 

 spore or from the one-celled spore a 

 thin tube grows out, increases in length 

 and enters the leaf by a breathing pore. 

 When inside it branches freely and gets 

 its nourishment from tne cells of the 

 leaf. After a period of eleven days the 

 translucent spot is clearly visible and in 

 40 



from six to eight days more the blister 

 is formed and hyphaa produce spores. 



If a blister is situated on the midrib, 

 the leaf often folds or rolls upon itself 

 irregularly, sometimes the lower and 

 sometimes the upper surface of the leaf 

 remaining outermost. If several blisters 

 occur near the margin, the leaf often 

 becomes curled and twisted in the 

 most fantastic manner. The number of 

 blisters on a leaf varies from one up to 

 about twenty, and they may be isolated 

 or several may run together to form a 

 large patch with an irregular outline. 

 To such an extent does this sometimes 

 go that the whole under-surface of the 

 leaf may be covered with an even mass 

 of blisters. 



When many of the leaves on a bush 

 have even only a few blisters each, the 

 damage done to the bush in reducing its 

 green surface available for food-making 

 is great and in addition the parasite is 

 draining the host bush of the nourish- 

 ment made for it by healthy leaf tissue. 

 When the vitality of the growth is 

 lowered the healthy flushing of the 

 young leaves and buds is retarded 

 causing considerable loss. When the 

 disease runs unchecked through a bush 

 and the young shoots have fallen over 

 and decayed, it has a black, unsightly 

 appearance quite justifying the anxiety 

 of the managers on those gardens where 

 the disease is prevalent. 



The exact place in the district where 

 the disease first occurred cannot now be 

 settled with certainty, but it was most 

 probably on the slopes on the southern 

 side of the Senchal Ridge. Last year it 

 was noticed at several places near the 

 head waters of the Balasan River almost 

 simultaneously. After it had once been 

 reported it was found on quite a number 

 of gardens. From this it may be con- 

 jectured that the rate of dissemination 

 of the disease was very rapid or that it 

 may have existed in the gardens for 

 some time without having been noticed. 

 This last may quite well have occurred 

 in gardens where it was doing little real 

 damage, especially as the disease was 

 new to the district and was then un- 

 known to many planters. From obser- 

 vations made this year the former also 

 seems to be the case, and when once 

 the blisters have matured the spores, 

 which they produced, quickly become 

 distributed. 



When blister-blight appears on a block 

 scattered bushes are affected, some badly 

 and others slightly. Only one or two 

 leaves on a bush or a few more or a great 

 many are blistered. A block may appear 

 quite healthy till suddenly a few blistered 

 leaves will be seen, and this occurs in a 



