448 



RESEARCHES ON FUNGI 



cojfeicola is seen to be composed of a bundle of hyphae, each 5-8 [x 

 thick, united with one another by numerous anastomoses. Further- 

 more, the outer surface of each hypha in a ripe gemma is verru- 

 culose oudng to the presence of crystals of calcium oxalate. Owing 

 to these structural features, a gemma is a very stiff rod, in conse- 

 quence of which under slight pressure it readily breaks off just 

 above the knob-like pedicel on which it stands. By the time a 

 gemma is ready to be set free, its hyphae contain a rich store of 

 glycogen. 



Even a slight wind is sufficient to break off the gemmae from 



Fio. 227. — Sclerolium coffeicola. Infected leaves of Coffea liberici which had fallen 

 iipon the ground. The mycelium has grown out from the leaf -spots centri- 

 f ugally over the surface of the leaf in the fonn of strands. The mycelial strands 

 on the left-hand leaf liave produced a number of gemmifers. Photographed by 

 G. Stahel. Natural size. 



their bases and carry them away. In plantations which are badly 

 affected with the disease, a number of gemmae can be seen lying on 

 every leaf, chiefly on the upper surface (Fig. 228), but not infrequently 

 also on the lower surface. In damp weather it is possible to observe 

 the gemmae infecting the leaves and forming new leaf-spots. 



When a gemma which has been blown on to a leaf begins to 

 develop, it first of all forms an appressorium, or sometimes two or 

 more. An appressorium is a solid mass of hyphae which assumes a 

 hemispherical shape and flattens itself out upon the epidermis. 

 When full-grown, it has a diameter of 0-05-0 -5 mm. The appres- 



