3 H. MARSHALL WARD. 



The external appearance of a leaf severely affected with the 

 " disease" is characterised as follows : — Small, cloudy yellow spots 

 appear on the under side of the leaf ; any one of these may be ob- 

 served to increase in area and depth of colour, spreading centri- 

 fugally from a point in a more or less circular manner. Sections 

 of such a spot show that a young mycelium is spreading in the 

 lacuuEe between the cells of the leaf, and that the discoloured 

 area corresponds to that occupied by the mycelium. In a few 

 days small groups of orange-coloured, granular bodies, appear 

 externally, and, rapidly increasing in numbers, soon form an 

 orange-red powder on the under side of the leaf; this pulveru- 

 lent ^' rust " consists of the -spores^ developed by the internal 

 mycelium. They arise in rosette-like groups from the stomata 

 to which the mycelial branches have direct access from within. 

 As age progresses the yellow colour of the " disease patch " 

 becomes darker, and at length brown in the centre ; the brown 

 colour, which is due to destroyed leaf cells, kc, spreads centrifu- 

 galiy as before, and at length a shrivelled, dark-brown blotch of 

 dead tissue is all that remains of the affected area. 



This is the typical mode of development of the " disease spot," 

 and there are several points of importance regarding it. The 

 oldest part is always the centre, and as we proceed outwards 

 from this, each successive phase is younger than the last. The 

 oldest part appears to be always on the under side of the leaf j 

 the discoloration of the upper side and the corresponding 

 appearance of the mycelium there occur later. The appearance 

 of various saprophytic fungi on the old shrivelled spot indicates 

 the completion of the destruction. With these and other phe- 

 nomena which vary the described course of the " disease spot " 

 we are not at present concerned. 



The orange-coloured " rust " consists chiefly of small, some- 

 what reniform bodies, which, from their structure, behaviour 

 towards reagents, &c., and especially from their manner of 

 germination, I have called Uredospores, to distinguish them from 

 a second, less common, napiform spore, which presents suffi- 

 cient analogies to the typical Teleutospore^ of the Uredinea to 

 warrant the adoption of that name also. 



The " Teleutospores " were discovered in Ceylon in March, 

 1880 f they occur mingled with the much more numerous 

 Uredospores on the same ''rust^' patch, and, indeed, spring 

 from the same spore-group. Mr. Abbay seems to have incom- 

 pletely figured similar bodies, without understanding their nature, 



' The evidence which proves this vrill be found below. 



" Vide 'Second Pieport to the Ceylon Government,' 1, 1880. 



3 Vide 'Preliminary Report to Ceylon Government/ June, 1880. 



