UROMYCES ALOES COOKE. 66l 



ments I succeeded in establishing the fungus on Aloe leaves ir. 

 one or two cases, though in many cases I was unsuccessful. 



The time from date of inoculation to the date of first appear- 

 ance of small whitish blisters on the inoculated leaves was about 

 a month ; the darkening of these pustules due to the ripening of 

 the spores was first noticeable about lo days later. 



I have failed up to now to discover the mode of entrance of 

 the fungus into the leaf, whether it be through the stoma, or 

 directly through the epidermis. Considering the thickness and 

 toughness of the latter in most Aloes, one would expect the 

 fungus to gain an entrance through the stomata. 



luuniDiity. — Biological varieties of Uromyces Aloes, if not 

 true morphological ones, may be found to exist within the 

 species, and this might account for the fact that some species of 

 the Aloe appear to be not as readily attacked as others. 



This is so in the case of Aloe arborescens, a rather succulent 

 soft Aloe. Plate i, however, shows a specimen of this Aloe which 

 is particularly badly attacked. The comparative immunitv which 

 this species enjoys ( i.e., those specimens of the species which are 

 growing on the rockeries in Pretoria) may be due to the fact that 

 the badlv attacked one mentioned above is growing only at some 

 distance from most of the specimens of the same species, 

 although these latter are themselves surrounded by very badly 

 diseased Aloes of various species. In this case it is probably a 

 varietal difference of morphological character in the fungus with 

 which we have to deal, evidence for which was brought forward 

 in the description of the TeleutoSpores. 



LITERATURE. 



T Cooke: Grc^illea. 20. i6 (Sept. t8oi). 



2. Hennines: Eneler : Botan.. Jahrb. Pd. 14 [4] (Dec. 1891). 



3. Magnus: Botan. GescUschaft 10, 48 (i8g2). 



4. W. B. Grove: "The British Rust Fungi." 



5 W. B. Grove: "The Evolution of the Higher Uredineae," New Phytolo- 



gist (191.3). . ^, . ^ „ . . 



6. Blackman : " On the Fertihsation. Alternation of Generations and 



General Cytology of the Uredinse." Ann. Bot., 18. 



7. Blackman: "On the conditions of Teleutospore Germination and 



Sporidia Formation in the Uredinese." New Phytologist',, 2 



(1903^ 



8. Christman: ''Alternation of Generations and Morphology of bpore 



Formation in Rusts." Bot. Gas. (1907)- ,^ 



9. Blackman & Eraser: "Further Studies on Sexuality of the Uredineaa, ' 



Anyi. Bot. 20. 



DESCRIPTION OF PLATES AND TEXT FIGURES. 



Plate 22 fl.— Photo of badly-attacked specimen of Aloe arborescens. 



Botanical Laboratories, Pretoria. Photo by Miss A. 



Bottomlev. 

 Plate 22 h. — Photo of leaf of Aloe arborescens; s shows positions of 



groups of spermogonia. 



