56 FIRST REPORT ON 7 ECONOMIC BIOLOGY. 



IRIS LEAF-BLOTCH. 



Heterosporium gracile (Sacc.). 



This is often a very troublesome disease on Iris germanica and 

 other species. In 1909 and 1910 it was particularly prevalent. 



The appearance of the mould is very variable according to the 

 particular species of host-plant and the season. Generally the upper 

 surface of the leaves turns brown and commences to decay ; roundish 

 or oval black blotches next appear from half to one inch in length, or 

 these may occur on leaves which appear to be perfectly healthy. 

 Sometimes the blotches are smaller and more numerous. In either 

 case, later, there develops on these areas a sooty-brown mould, con- 

 sisting of short, thick, jointed threads, which bear conidia. These 

 latter vary in size, are usually transversely divided once or twice, the 

 surface of each cell being covered with minute points. The conidia 

 germinate freely, and if left undisturbed the disease spreads rapidly. 



Spraying with sulphate of copper has been recommended, but 

 I have obtained excellent results with potassium sulphide, an ounce 

 and a half to every three gallons of water and one ounce of soft soap. 

 It is all important that the spraying should be commenced immediately 

 the brown blotches on the leaves appear, and repeated three or four 

 times at intervals of three or four days. 



HYACINTH YELLOW DISEASE. 



Pseudomonas hyacinthi (Wakk.). 



There is no more troublesome or serious disease attacking 

 hyacinths than the one here mentioned. A lengthy investigation has 

 been made and is still being continued. So far the facts point to the 

 disease being due to the Pseudomonas, which appears in the autumn 

 in masses of slime in the vascular bundles. In the spring they make 

 their appearance in the vascular bundles of the leaves, and the plants 

 quickly die. Very often the bulb rots away before. 



Associated with, and swiftly following, the attack of the bacteria 

 is a fungus called Hypomyces hyacinthi. 



Diseased bulbs usually contain a number of kinds of bacteria, 

 as well as the familiar mould Penicillium glaucum, all of which tend 

 to make investigation difficult and somewhat complicated. 



