Pomona College Journal of Economic Botany 



251 



stage and develops tougher and longer leaves it is, as far as I have been able to 

 observe, immune. The infection has been found to be especially noticeable upon 

 the tender leaves of the shoots and sprouts from old eucalyptus stumps and here 

 perhaps it works its greatest damage. There have come to my notice such shoots 

 twentj' feet in height on which there seemed not to be a single leaf that has 

 escaped the infection. Many of the leaves had turned yellow except where the 

 great blotches of diseased tissue were bearing their harvest of countless spores. 

 In a five acre Blue Gum stand just south of Claremont there was not a tree to 

 be found on which the young leaves were free from the fungus. In spite of this 

 general infection the actual damage caused was not great. The number of young, 

 broad leaves were few in comparison to the tougher ones and the trees did not 

 seriously miss their failure to function. 



The infection probably takes place through the stomata on the under side 

 of the leaf and with the spread of the mycelium the leaf tissues are killed. The 

 presence of the fungus is first noticed by the appearance of small circular or 

 irregular purplish-brown patches on the lower epidermis. As the mycelium 

 spreads the diseased area extends from epidermis to epidermis and in case of 

 bad infection the areas merge together in large irregular shaped blotches. In 

 the older spots the color of the center changes to grayish-brown, while the edge 

 retains the characteristic purplish-brown marking. At this stage the pycnidia 

 are formed just beneath the lower epidermis (Figure 108 A). The pycnidia are 

 black granular bodies, globular in shape and ranging in diameter from .06 to 

 .12 mm. Thej' appear at times in pairs and again solitary. In one small diseased 

 area 1 mm. across occurred ten of these pycnidia in all stages of development. 

 At times they attain large size extending fully three-fourths the distance through 

 the leaf, crowding and distorting the palisade cells. The pycnidial wall is made 

 up of a rather thin but quite tough granular membrane (Figure 108 A). 



The spores vary noticeably in size though but little in their general shape 

 (Figure 108 E). They are borne upon short, simple, hyaline sporophores (Figure 

 108 A) ranging from 6 to 10 microns in length. The spores themselves vary in 

 size from 8 to 1 1 by 22 to 32 microns and have three transverse septa, the wall 

 of the spore being depressed at each septum. In color they are olivaceous to 

 smoky brown. 



Wlien the pycnidium is mature the epidermis is ruptured and the spores 

 emerge in a compact, naked, black mass which adheres loosely to the epidermis, 

 and these masses are noticeable as minute black dots upon the surface of the 

 diseased area (Figure 108 B). 



This apparently undescribed species may be called Hendersonia eucalypticola. 



