52 THE BOOK OF THE IRIS 



account of it is given by Dr M. C. Cooke in the Journal 

 of the Royal Horticultural Society, vol. xxvii. p. 398, and 

 in plate v. it is represented by figure 92. It is described 

 as a black mould which forms crust-like patches on the 

 outer sheath of the bulb, gradually spreading to every 

 part. Dr Cooke says that, " Soaking the bulbs for two 

 hours in a solution of one part formalin to three hundred 

 parts of water will destroy the fungus, so long as it is 

 external, and has not penetrated deeply into the bulb." 

 If this has happened, no doubt the bulbs should be 

 burnt, and a new stock obtained for planting in a new 

 position. The original description of this fungus is by 

 Mr Geo. Massee in the Gardeners' Chronicle of June 

 1/j.th, 1899, p. 412, where it is also well illustrated. 



Iris Leaf-blotch, caused by Heterosporium gracile. 

 This disease is described by Dr Cooke with the last, in 

 the Journal of the Royal Horticultural Society, vol. xxvii. 

 p. 398, and also in vol. xxvi. p. 45- ^ n t ^ ie volume 

 first quoted, on plate v., it is represented by figure 90. 

 Dr Cooke says that for some time past the foliage of 

 Iris germanica has been suffering in many places from 

 this mould, which appears at some seasons with as- 

 tonishing vigour, ultimately destroying the plants. The 

 leaves become spotted with elliptical or oblong fuscous 

 spots about a quarter of an inch in length, a little darker 

 at the edge. At length these spots become confluent, 

 until the whole surface of the leaf is brown and dead, 

 whilst the original fuscous spots remain of a paler colour 

 than the surrounding tissue. Often there is no exter- 

 nal evidence of the presence of any parasitic mould upon 

 the spots, especially on the spots occurring in the 

 spring, but there is a plentiful fungoid mycelium in the 

 tissues. Ultimately some of the spots, towards the 

 centre, are dotted with little black dots, like pin-points, 

 which represent the mature condition of the black mould 



