IRISH GARDENING 



163 



Fig. 2. 



containing eight spores. As ripening proceeds, 

 these spores are emptied from their sacs, and are 

 finally extruded from the perithecium through 

 a small pore at its apex. These spores, if they 

 find lodgment in a crack or wound in the bark 

 of the tree, germinate there and produce canker. 



All gardeners are familiar with the "" knife " 

 treatment (followed by tar or paint) for the 

 type of canker desciibed, and the object of the 

 present note is not therefore to go into detail 

 in this connection, but rather to call attention 

 to an earlier and much more infectious phase of 

 the disease which, as stated above, is by many 

 gardeners not recognised as canker at all. This 

 is perhaps scarcely surprising, seeing that the 

 earlier mycologists^themselves looked upon this 

 stage as being due to quite a different fungus 

 to which they gave a name of its own. 



Fig. 2 clearly shows the condition of things in 

 the early stages of canker. The bark — nearly 

 always at a branch or near a bud — is dead over 

 a more or less circular or oval area. It is 

 commonly more or less wrinkled into con- 

 centric zones, and bursting through it are to be 

 found numerous small pustules of a whitish 

 colour. The base of each of these pustules is 

 made up of a dense mass of fungus threads, 



while 011 the outer free surface countless myriads 

 of spores are produced which are washed down 

 the twigs by every shower of rain, and, gaining 

 entrance into the bark through wounds or insect 

 punctures, establish fresh centres of canker. 



Fig. 3 is a photo micrograph of a thin section 

 cut with a razor through a small portion of the 

 bark bearing one of these pustules, and it shows 

 clearly the way in which the cushion-like mass 

 of the fungus has burst aside the outer layers of 

 the bark in its endeavour to reach the exterior 

 (to the right) so that its spores may be free to 

 become dispersed. The magnification is not 

 sufficiently great to show the spores themselves 

 individually. The earliest formed spores are 

 very small and single-celled, but soon these are 

 replaced by much longer, almost thread-like, 

 spores each composed of several cells, and each 

 therefore providing several chances of infection 

 at a wound. 



tt is this early and highly infectious stage of 

 canker that is so frecprently overlooked, and, of 

 course, the question at once arises, how can this 

 important source of infection be dealt with ? 

 The remedy is simple, but requires patience and 

 perseverance. Take a small brush, such as a 

 penny earners hair paint-brush, and paint over 

 each affected area, taking care as far as possible 

 not to wet the still healthy bark with either ordi- 

 nary paraffin oil or with methylated spirit. The 

 former liquid can be used in dry, the latter in 

 either drv or wet weather. If this be done not 



Fig. 



only will the spores be lulled, but the fungus 

 spawn within the bark will also be destroyed, 

 and the development of the second stagein the 

 canker cycle at these places will be inhibited. 



G. H. P. 



