448 DISEASES OF CULTIVATED PLANTS 



Orchid leaf spot (Hypodermium orchidearum, Cke. and 

 Mass.) forms minute, blackish, elongated spots on living 

 leaves of Cymbidium eburneum. The spots are arranged in 

 groups, often extending for a distance of one to two inches, 

 and at these points the leaf turns yellow and dies. When 

 the spore-clusters burst through the epidermis they are 

 blackish owing to the dark-coloured fungus mycelium. The 

 spores are hyaline and produced in chains, but soon separate 

 from each other in contact with moisture. They are narrowly 

 elliptic-oblong, and measure 25-30 x 5 /*. 



Sponging the leaves with a rose-coloured solution of per- 

 manganate of potash destroyed the spores, and checked the 

 spread of the disease. 



LIBERTELLA (Desm.) 



Spore-masses of various form, covered by the epidermis, the 

 conidia usually escaping in a coloured, mucilaginous tendril, 

 slenderly fusiform, elongated, continuous, hyaline. 



Fig-tree canker [Libertella u/cerata, Mass.) is frequently 

 the cause of very serious injury to fig-trees grown under glass. 

 Soon after a given point of stem or branch is infected the 

 bark shows minute, radiating cracks, which gradually increase 

 in size until eventually a large cankered wound results, the 

 bark and sap-wood being completely eaten away. If the 

 wound is confined to one side of the branch, the latter may 

 continue to live for some time, but if, as is frequently the 

 case, the branch is girdled, the portion above the wound dies 

 almost at once, and soon becomes more or less covered with 

 the fruit of the fungus, which oozes out of the dead bark in 

 the form of very minute hairs or tendrils consisting of myriads 

 of very minute conidia held together by a mucilaginous sub- 

 stance which becomes hard and rigid when dry, but melt and 

 are dispersed by rain or dew. 



Pustules gregarious, numerous, minute, developed under 

 the epidermis, which is eventually ruptured, the tendrils of 

 conidia of a pale colour, oozing into the air ; conidia fusiform, 

 ends acute, continuous, curved, hyaline, 55-60X4/'. 



No higher stage has as yet been connected with this coni- 

 dial form. 



No success attended attempts at infection with conidia on 

 an unbroken surface of a branch, whereas infection followed 

 the placing of conidia in minute punctures. A knife that 



