DISEASES OF PLANTS. 



83 



its presence, and in addition to robbing the plant of a certain 

 amount of material elaborated for its own use, proves injurious 

 in rupturing the epidermis in many places, and thus facilitating 

 the escape of water from the leaf, and, as a consequence of which, 

 the balance of absorption and transpiration is upset. This 

 fungus may be considered as a very simple type of parasite, 

 inasmuch as, so far as is known, only summer- spores are formed, 

 but as the leaves of orchids are always present, the spores find a 

 suitable place for germination throughout the year ; secondly, 

 the fungus completes its development on one and the same host- 

 plant. 



(1) Portion of au orchid leaf showing the disease : natural size. (2) Portion of a 

 diseased patch, slightly magnified. (3) A fungus fruit showing the spores escaping in the 

 form of a tendril ; more highly magnified. (5) Section or slice through a fungus fruit im- 

 bedded in the substance of an orchid leaf ; highly magnified. (5) Spores of the fungus ; 

 magnified -1UU times. 



Inoculation takes place by the spores being conveyed by 

 some means on to the surface of a damp orchid leaf, germina- 

 tion takes place at once, and within a few hours the germ-tube y 

 or first-formed mycelium produced by the germinating spore 



Fig. 1.— Orchid Leaf Bust (Glceosporium cinctum). 



G 2 



