GALLS CAUSED BY FUNGI 119 



the place of bracts in pistillate flowers of the Common 

 Alder. These peculiar galls result from the presence of 

 Exoascus alnitorqum ; they are sometimes 30 mm. long, and 

 as many as ten small ones may occur on a single catkin. 

 They may be found from June to October, but are rare 

 in Britain. Alder trees abound at Haslemere, but I have 

 never succeeded in finding the galls in this district. 



In the latter part of May and throughout June Nettles 

 afflicted with the aecidial stage of Puccinia caricis axe fre- 

 quently met with. The gall which arises is very noticeable ; 

 the condition is well shown in Plate XVI., Fig. 2. The 

 stem becomes greatly swollen and bent; immersed in the 

 swollen tissue are the bodies (pseudoperidia) containing the 



Fig. 33 — Female Catkins of Alirns glutinosa, the Upper 

 GALLED BY Exottscus aluitorquus. 1/2. 



orange-yellow aecidiospores. The fungus also fruits on the 

 leaves, forming yellow spots. It is heteroecious, and the 

 aecidial stage is known under the name of Aecidium urticae. 

 The aecidiospores are carried to various Sedges, on which 

 the teleutospores are produced from July to April. 



On the same plate (Fig. 3) may be seen grass stems 

 attacked by the " Reed Mace " fungus, Epichloe typhina. 

 Afflicted plants do not flower, and growth is seldom pro- 

 longed above the galled part, which is usually the upper leaf 

 sheath. Upon its first appearance on the stem the fungus 

 is a thin whitish crust ; it becomes yellow later, and is then 

 studded with the mouths of the perithecia immersed in the 



