CHAPTER XXII 

 The Ascospore and Other Fungi 



A NUMBER of parasitic fungi are classified together in a 

 group called Ascotnycetes because the principal spores are 

 developed in special tubular spore cases called asci ; these 

 spores are called ascospores. They often serve as a means 

 by which the fungus passes through the winter ; so they 

 are sometimes spoken of as winter spores. The fungus may 

 also develop more temporary spores which are often spoken 

 of as conidiospores or summer spores. 



Black Knot 



Most schoolboys have seen the branches of plum and 

 cherry trees distorted by a black, knotty growth, having 

 the appearance of the picture on the opposite page. Wild 

 cherry trees very commonly show the injury, which is pro- 

 duced by the fungous disease known as the Black Knot. 

 The knots are caused by the growth of a parasitic fungus 

 in the twigs or larger branches. They first appear as 

 swollen places on the bark. These enlarge and cause 

 irregular cracks which are characteristic of the disease. 

 Finally the whole circumference of the twig may be affected 

 so that the part beyond soon dies. 



During warm weather vast numbers of summer spores 

 are produced upon the bark of the knots. These give the 

 affected part of the twig a soft, velvety surface of a dark 

 olive color. These spores are blown from place to place. 



242 



