CHAPTER III 



THE LARCH CANKER (continued) 



The reproductive organs of the fungus. Germination of spores. Pure 

 cultures on nutrient media. Artificial infection with canker. 



The reproductive organs of the fungus. The reproductive 

 organs are of two kinds : 



1. Apothecia. 



2 . Spermogonia or pycnidia, the name depending on the 

 interpretation of their morphological nature. 



When fructifications are about to be formed there first 

 appear on the surface of the bark a number of white or pale 

 yellow felt-like mycelial outgrowths. These may give rise 

 to both apothecia and spermogonia, the latter being generally 

 mature just at the time when the former are initiated. 



Apothecia. The youngest stage which I have traced in 

 the formation of apothecia consists in a group of hyphae 

 standing out from a small portion of one of the mycelial 

 masses on the surface of the stem. These hyphae are easily 

 distinguished by numerous very fine wart-like outgrowths 

 on their walls. The portion bearing them is circular in 

 outline, and towards the centre the hyphae are bent inwards. 

 Underneath these hyphae there next appears the first 

 indication of a layer of hyphae directed at right angles to 

 the surface. This layer, which is the young hymenium or 

 ascus-bearing layer, becomes broadened by the interpolation 

 of fresh hyphae, and the apex of the apothecium opens, 

 leaving the warted hyphae as a broad fringe of hairs round 

 the hymenium, which is orange in colour. 



The apothecium grows for a long time, reaching a size of 

 2 -4 mm., or in extreme cases 5 mm. The hymenium becomes 

 paler with age, and the margin and under- surf ace are white 

 throughout. The whole is raised on a short stalk about 

 1 mm. in height and rather less in thickness (fig. 17). 



