27 



STUDIES IN BACTERIOSIS. HI. 



A BACTERIAL LEAF-SPOT DISEASE OF PROTEA 



CYNAB0IDE8, EXHIBITING A HOST REACTION 



OF POSSIBLY BACTERIOLYTIC NATURE. 



By SYDNEY G. PAINE and H. STANSFIELD. 



{From, the Department of Plant Physiology and Pathology, Imperial 

 College of Science and Technology, London.) 



(With Plate n.) 



The disease was observed on plants of Protea cynaroides^ in the houses at 

 Kew Gardens where, for a number of years — practically since the intro- 

 duction of this species to the Gardens — it has caused considerable dis- 

 figurement to the plants. It occurs on the leaves of all the older plants 

 and shows itself on the leaves of seedlings when these have reached a 

 height of some 10 or 12 inches. 



Symptoms or the Disease. 



The disease is characterised by numerous dome-shaped blisters of a 

 reddish-brown colour scattered promiscuously over the lamina of the 

 leaf, mainly, though not entirely, upon the upper surface. They vary 

 in diameter from one to three millimetres and the surface of the blisters 

 is raised half to one millimetre above the general level of the leaf. On 

 the younger leaves in place of the brown blisters there occur rather wider 

 areas whose surface is frequently depressed by shrinkage of the under- 

 lying cells. These areas have a diameter up to five or six millimetres, and 

 still larger patches arise through the coalescence of several such spots. 

 The colour of these depressed areas is much brighter than that of the 

 blister- like spots and is either a uniform red or a reddish-brown surrounded 

 by a zone of bright vermiHon. The vermilion colour is very conspicuous 

 when the leaf is held up to the light. On examination in this way by 

 transmitted light every spot exhibits a clear translucent halo in a zone 

 of one or two millimetres round the spot. The appearance of the diseased 



