NOTES ON THE MORPHOLOGY AND LIFE HISTORY 

 OF UROMYCES ALOES COOKE. 



By Victor Armsby Putterill, B.A. 



{Read, July lo, 1918.) 



(Plates 22, 23, and six text figures.) 



The fungus which causes " rust " in Aloes was first described 

 by Cooke in September, 1891, from material sent him by the 

 late Dr. Medley Wood, collected at Mooi River, Natal, and was 

 named by him Uredo (UromycesF) Aloes Cooke. Some two 

 months later the same fungus was described by P. Hennings from 

 material collected by Schweinfurth in Abyssinia, and given the 

 name Uromyces aloicola. This dual nomenclature was noticed in 

 1892 by P. Magnus, and seeing that Cooke's species name had 

 the priority, the fungus was accordingly called Uromyces Aloes 

 Cooke, Magn. 



The existing descriptions of the fungus are occupied entirely 

 with, its field characters and the nature of the spores. Cooke's 

 description reads as follows : — 



Spots suborbicular or confluent; pallid; sori convex; large circinating 

 or clustered on the spots, often confluent ; for a long time covered ; 

 spores elliptical or subglobose. Smooth with a thick epispore (25 — 30 X 

 30/i) ; pedicels hyaline. 



As nothing further was known of the morphology and life- 

 history of the fungus, this investigation was undertaken on the 

 suggestion of Dr. Pole Evans, Chief of the Division of Botany, 

 at the Botanical and Pathological Laboratories, Pretoria. The 

 disease is abundant on the Aloes planted out on the rockeries and 

 in the gardens. The fungus has a wide distribution, similar 

 to that of its host. 



Appearance of the Disease. 



In leaves not badly afifected, in contrast to the appearance of 

 the healthy leaf, isolated circular patches of a pallid yellow 

 colour, anything up to 2 cm. in diameter, stand out clearly. The 

 edges of these patches mark within a millimetre or two the limits 

 of the spread of the mycelium in the tissues of the host. In 

 badly attacked leaves, these areas become confluent. (PI. 23 a 

 and h.) Dome-shaped pustules, a millimetre more or less high, 

 mark the position of the teleutospore sori ; at first they have the 

 appearance of white blisters; later they darken and rupture, 

 liberating the spores, which are produced in vast numbers. {PI 

 23 a and h; Fig. i a.) 



The vegetative cells of the mycelium are uninucleate; the 

 nuclei are typical, having a large deeply-staining nucleolus, the 

 rest of the nucleus appearing as a rule as a clear vacuole around 

 it. Haustoria take the form of branched tubes within the cells. 



