1893.] MICROSCOPICAL JOURNAL. 195 



IV. — Characters of the Fungus. 



Examination of one of these spots with a hand iens will show 

 that the tissues of the affected leaf are shrunken, making the 

 border of the spot on the side where the spores of the fungus 

 appear elevated. In the spots small threads that resemble fine 

 hairs can be seen readily. Cross section through a diseased 

 spot shows that the tissues are considerably shrunken (Plate 

 III, fig 2); and of brown color. On both sides of the leaf, brown 

 threads (conidiophores) pass out usually through the stomata. 

 Frank states that the conidiophores or branches, which bear the 

 spores, always pass out through the openings of the stomata. 

 This is said not to be the case in a fungus {Fusarium betse Rnbh,) 

 closely related to Cercospora. In Fusarium betee the tli reads 

 do not come through the stomata, but along side of it, break 

 ing the epidermis. Von Thuemen states that the conidiophores 

 of Cercospora break through the epidermis. Sorauer makes a 

 similar statement. I find, however, that the conidiophores not 

 only pass out through the stomata, but also break the epider- 

 mal cells (Plate III, fig. 3a). The conidiophores seldom occur 

 singly, they are clustered or fascicled, usually simple, but in 

 leaves which have been kept moist they are occasionally 

 branched (Plate III, fig. 5). They are divided into c^lls, and 

 at the upper end are knotty. The conidiophores arise from a 

 mass of short cells of the fungus situated immediately under- 

 neath the epidermis. Coming from these short cells and pass- 

 ing into the tissues of the leaf is the mycelium, which at first 

 vegetates between the cells of the leaf in the intercellular spaces. 

 It destroys the cells, causing them to collapse and take on a 

 brown color. The reproductive bodies are borne on the brown 

 threads at certain definite pointa (Plate IV, figs. 3 and 4). The 

 irregularities on the branches are due to the spores, which have 

 fallen, leaving a little scar. The spores are long cylindrical 

 bodies which taper towards the extremity. They vary greatly 

 in length ; in recently diseased green leaves they are short, but 

 in black and damp leaves they are very long ; they are plainly 

 many-celled. When leaves are kept in a moist place the spots 

 take on an ash gray color, owing to the immense number of 

 spores which are formed. These are readily seen with a hand 

 lens and look like plant hairs. When placed in a moist cham. 



