1899.] PUBLIC DOCUMENT — No. 33. 157 



tions ; and, in order to ascertain whether the trouble with 

 which we were concerned was the same which he had briefly 

 alhided to, we forwarded him specimens for examination, 

 which resulted in establishing the identity of the two. 

 There is a certain rescml)lance l)etween the spots which give 

 rise to bronzing and those which are caused by the black 

 spot; and we found that the impression prevailed among 

 some rose growers that bronzing w^as simply an innnature 

 stage of the black spot. To any one thoroughly familiar 

 with the characteristics of both diseases, the differences be- 

 tween them would bo evident, and they would not l)e likely 

 to confound one with the other. 



The investigations of Mr. Montgomery showed that the 

 abnormal condition of the rose leaves subject to bronzing 

 was not in any way connected vnth fungi, but is of a physio- 

 logical nature, or structural weakness, as Professor Halsted 

 had correctly surmised. The first symptoms are manifested 

 in a mottled, bronzing (coloration of the leaf. These spots 

 subsequently become more prominent, ranging from one- 

 sixteenth of an inch to one inch in size ; the infected por- 

 tions of the leaf frequently turn yellow, and eventually the 

 leaflets and leaf stalk droj) to the gi'ound. Sometimes, how- 

 ever, a whole leaflet becomes bronzed, and the yellowish 

 color is not observed. Numerous microscopic cross-sections 

 made of the bronzed leaf spots showed that the epidermal 

 and adjacent cells were in an abnormal condition. The 

 living contents of the cells were disintegrated, the proto- 

 plasm and cell walls had turned a reddish-brown color, and 

 numerous very minute bodies about the size of micrococci 

 filk'd the aft'ected cells. These minute bodies proved upon 

 examination to be crystals of calcium oxalate. The exces- 

 sive deposits of calcium oxalate indicate that the leaf cells, 

 being unable to obtain suflicient nourishment, were not al>le 

 to assimilate the calcium salts, and c()nse<|uently it is de- 

 posited in the cells in the form of calcium oxalate. It may 

 be said that all of this phenomenon is nothing extraordinary, 

 but merely concomitant with ihe death of the loaf, and can 

 be observed in other species of plants. ]\Ir. Montgomery 

 states that the bronzed leaves an; more susceptible to disease. 



