INJURIES INDUCED BY PLANTS 135 



Exoascus Betulce (Ascoinyces Betulce} produces bladder-like 

 outgrowths on the upper side of the leaves of the birch. 



Exoascus carnea produces globular bladder-like swellings on 

 the leaves of the birch. 



Exoascus aureiis* ( Taphrina aurea, T. Populi) produces golden 

 yellow outgrowths on the leaves of Populus nigra (Fig. 73) 

 and pocket-like outgrowths on the ovary of P. tremula and 

 P, alba (Fig. 74). 



Exoascu's Carpini produces witches' brooms on the hornbeam 

 (Fig. 75). 



Exoascus ccerulescens (As ' corny 'ces ccerulescens) produces bladder- 

 like swellings on oak-leaves. 



Exoascus Ulmi produces outgrowths on the upper side of elm- 

 leaves. 



IMPERFECTLY KNOWN ASCOMYCETES t 



The number of those fungus-forms with all of whose stages 

 of development we are not yet acquainted is an extremely 

 large one. In particular a large number of fungi are known 

 to us with whose gonidia whether on sporiferous hyphae or in 

 closed organs (pycnidia, spermogonia) we are familiar, but of 

 whose ascophores we are ignorant, so that we are unable 

 systematically to classify them. 



A few of the more important species that occur parasitically 

 on trees, especially on forest trees, may be referred to here. 



CERCOSPORA ACERiNA. 1 THE MAPLE-SEEDLING FUNGUS 



In rainy years a disease is sometimes conspicuously prevalent, 

 both on maple seedlings in the nursery and on those which have 

 sprung up naturally. It is to be recognized by the cotyledons 

 and first leaves, and also by the shoot axis, becoming black 

 and decomposed, or, if less severe, merely by black blotches 



1 R. Hartig, Untersuchungen, I. p. 58. 



*[l have found this species deforming the ovaries of poplars in Surrey. 

 ED.] 



f[No group of fungi offers more* opportunities to the investigator anxious 

 to add to our knowledge of pathogenic forms than the numerous " imperfect " 

 ascomycetes so common on our trees, &c. ED.] 



