166 



ASCOMYCETES. 



This is supported by Smith's investigations, in which an an- 

 atomical comparison of diseased twigs of peach and almond 

 showed no difference in the pathological effects. 



Exoascus crataegi Fuck, occurs on Ci'ntin-i/n.s Oxy<t<'<nifli<i. 

 and causes red swellings on the leaves and flowers, accom- 

 panied by hypertrophy of shoots in which the mycelium 

 perennates. 



Exoascus Tosquinetii (West). The deformation caused by 

 this species is frequent on the black alder (Ainu* <jl utinosa}. 

 The thickened, elongated, wrinkled twigs render attacked parts 

 very conspicuous in contrast to the normally developed parts of 



the tree. The leaves may be 

 wholly attacked and much 

 enlarged, or they may only 

 be hypertrophied at places so 

 as to form pustule-like swell- 

 ings. The epidermal and 

 mesophy 11 -cells of diseased 

 leaves become greatly en- 

 larged. 



Exoascus aureus (Pers.). 

 The leaves of the black poplar 

 (Pop i' In* nigra) attacked by 

 this parasite exhibit pustules 

 (Fig. 62). The asci are 

 formed as a golden coating 

 on the concave side of the 

 pustules, which is, in most 

 cases, the under side of the 



.. Leaf of Popuiu* leaf > rarely the ll PP er - The 

 T& S deT) inf e pl " cells forming the pustules 



have thicker walls and a 



somewhat different shape from the normal epidermal cells, and 

 they are not unfrequently sub-divided by walls of secondary 

 origin (Fig. 63). 



According to Smith, the cells of the palisade parenchyma have 

 also thickened walls, as well as being elongated and occasionally 

 chambered ; the cells of the spongy parenchyma are enlarged and 

 have thicker walls ; so also are the cells of the collenchyma of 

 the leaf venation. 



