io8 prp:sidentiai. al)Dri:ss — si-xtion c. 



phyto-bacteriolo; y is ])cconiing- a subject of such vast importance 

 that even at present it may be looked upon as a science of its 

 own, as is evident from the large output of literature dealing- 

 with this branch of research. 



At some future date 1 hope that this whole question of plant 

 bacteriology may be dealt with by Dr. Doidge, wdio has alread> 

 made a special study of the subject, and who will be able to 

 handle it far more skilftilh- than it would be ])ossible for me to 

 do. 



At this meeting" Dr. Doidge will bring to ycnu" notice two 

 bacterial diseases which, so far as we at present know, seem to 

 be peculiar to South Africa. There is the bacterial spot of citrus, 

 caused bv Bacillits cilriiinu-iilans Doidge, and which appears to be 

 confined to the Cape Province. 



There is also the bacterial blight of pear Ijlossom, ])revalent 

 in the Cape and other ])arts of South Africa. 



To me it seems more than probable that when the research 

 work that has been done on these diseases is more generally 

 known, these troubles ma\ be recognised in other jxirts of the 

 world. As an illustration, ! might quote a rather important citrus 

 disease which w^as first detected and described by myself from 

 this Province in 1909, and was referred to as " black rot "' of 

 Natal citrus fruit. The causal organism was determined and 

 described as Diplodia iiatalensis Pole Evans. At that time it was 

 unknown in any other part of the world. Since then the same 

 disease has been found in Florida, Cuba, and Porto Rico, where 

 it not only causes a decay of citrus fruit, but produces a gum- 

 ming of citrus trees, and to which i'oiuelo are most susceptible. 

 It has als(t l)een sliown to lie the cau<e of gtimmosis in ])each trees 

 in Florida. 



One serious Ijacterial (li.--ea>t:, that due to Bacillus iiiangi- 

 ferce Doidge. whicli catises a rot of the mango fruit, must, how- 

 ever, in the light of our present knowledge, be looked u|)on as 

 peculiar to South Africa. This parasite has practicalh ruined 

 one of Scnith Africa's promising fruit industries. 



1 will now select a few of the more important economic 

 ijroblems in m)cology which have received attention during the 

 past ten years. 



Till''. C'|':i:i;ai. Ki'sts. 



Up to 1905 little was known about the rusts present on 

 cereals in South Africa. For years past crops of wdieat, barle}-, 

 and oats had been ruined by this pest. In fact, in some localities, 

 the cultivation of these crops had l)een abandoned on account of 

 rust. 



This i»roblem is one to which i have devoted sonu- attention. 

 ard from observations extending over a period of five years 

 we now know that — 



