10 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



of a more fundamental nature. Under these circumstances the 

 leaf will probably fall, though this result is not due, or at any 

 rate only in a minor degree, to the class of injury included under 

 this paragraph. 



B. Cases in which leaves fall, showing either a complete dis- 

 coloration (brown or yellow), or only a partial discoloration, 

 limited to the apex, or margins or base, or in which the dis- 

 coloration is restricted to minute specks or to irregular patches 

 scattered over the surface, or the leaf may fall green and 

 apparently uninjured. We must include here also cases in which 

 the lamina is affected in any of the ways just indicated, but in 

 which the leaf does not disarticulate, but remains, withered and 

 attached to the plant. Instances of disarticulating leaves are 

 innumerable, but whether this is preceded by local or general 

 change in colour, or whether the leaf falls quite green, depends 

 upon a variety of circumstances. Plants in which the leaf does 

 not fall, but remains attached as described, are rare. Bouvardia 

 and Centropogon Lucianus may be quoted. 



I shall distinguish between these two classes of injury, 

 because I believe them to be due to distinct causes. 



The injuries to flower-buds and flowers I have described and 

 discussed under Section III. 



Further Notes on Class of Injuries A. 



The local blotchings indicated under A are due, I apprehend, 

 to the action of an acid upon the upper surface of the leaf. The 

 leaf here presents all the characters of being attacked from with- 

 out. In the first instance these markings »are limited to the 

 upper surface, or if they involve the lower surface also, this is 

 strictly confined to the portions immediately adjacent to the apex 

 of the leaf. The fogs deposit a layer of dirt upon the surface, 

 which may or may not include sufficient poisonous substances to 

 effect a general corrosive action upon the upper epidermis. But 

 in horticultural practice the frequent wetting of the leaves leads 

 to certain constituents of the deposit being taken up by the 

 water, which, as is well known, has a tendency to collect at the 

 margins, and especially at the tips of the leaves. One may walk 

 through a conservatory and shake off drops from every plant. 

 The moisture gradually evaporates, leaving behind what was 

 dissolved in it. The process is, no doubt, repeated time after 



