122 



Microscopic examination of this new surface does not show any 

 stomata, and there are no oil glands. The mycelium of the fungus 



appears to be confined to the scab, and 

 it would appear that in the struggle for 

 mastery the tissues of the orange come 

 off best, so that the scab is shed. 



The reason for the difficulty in the re- 

 moval at the small points mentioned is 

 that at these points the scab seems to be 

 sunk deeper into the skin, for when it is 

 removed there is left a small depression. 

 Fig. 132 shows a cross-section through 

 one of the depressions where the scab 

 : > has its firmest attachment. 



Fig. 132 Depressed portion of the gray In addition to the fungus filaments 

 SLS'tSUh^eltShS^ and the comdia which they bear, there 

 the scab and a portion of the rind of mav be found in the scabbv matter 



the orange: a, the attachment point , J ,,-, -,1 ! . , i 



of the fungus ; b, the surface of the spherical penthecia with a distinct ostiole. 



The perithecia measure 100/x, and the 



ostiole 15/x. On the leaves of trees bearing scabby fruit of this sort are 

 sometimes to be found smallish spots which eventually become gray 

 and papery, and this papery part at last falls out, leaving a " shot 

 hole." The perithecia to be found in these papery tissues are of the 

 same size, form and structure, as those in the gray scab. The spores 

 derived from the perithecia on the leaves measure 7 x 2*6/x. 



Cladosporium of the Orange- 



Specimens of fruit and foliage of the orange have been received, 

 somewhat attacked by a fungus belonging to the genus Cladosporium. 

 I could not be certain whether this fungus disease was causing much 

 damage. My doubt was increased in this case by the presence of a 

 considerable number of scale insects on the specimens examined. 



I am not aware that this particular species of Cladosporium found on 

 the citrus trees has ever been specially treated with fungicides, and it is 

 therefore impossible to say with absolute certainty what the results of 

 treatment will be. There is, however, no reason to doubt that the 

 application of Bordeaux mixture as for AJelanose (?) will be entirely 

 successful. The Cladosporium of the citrus tribe is so much like that of 

 the peach and other stone fruits, as to make me believe that what will 

 answer for one will answer for the other. It is known that Bordeaux 

 mixture is efficient for the Peach Freckle, Cladosporium carpophilum* 



DISEASES EITHER CAUSED BY OR ASSOCIATED WITH BACTERIA. 



IT is now coming to be an accepted fact that bacteria are responsible 

 for a number of diseases of plants. A dozen years ago there was hardly 

 a single authenticated and well-known instance of such a disease, and 

 even to-day the dispute continues in some quarters as to the trust- 

 worthiness of the evidence on this matter. Most of the instances- 

 mentioned below belong to the more authentic class of bacterial diseases 

 of crops, though some are still in need of further investigation. 

 Those who doubt the possibility of microbes being the cause of 



