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fall of the spore-masses (telia) is covered by a scar-tissue consisting 

 of several layers of cork-cells, and that the new spore-masses form- 

 ing in succeeding years rarely break through this cork layer of 

 an old scar but issue through some new portion of the bark. 

 Some of the typical gall-producing forms arise as outgrowths 

 from branches or twigs (as G. globosum. and G. Nehoni) while others 

 may have their origin in the leaves. G. Juni-peri-virginianae and 

 G. floriforme are examples of species which produce galls that origi- 

 nate in the leaves. Sanford (1888) investigated the changes which 

 are induced in leaf-tissues by the formation of a globoid or reni- 

 form gall of G. Juniperi-virginianae with the following results: 

 the most striking change is in the great multipication of cells and 

 their generally enlarged size; the cell-walls are thicker than normal 

 and behave toward cytological reagents decidedly like fungous tis- 

 sue; the vascular system is developed until it is as important as in a 

 branch and divides in a peculiarly radiating manner, the elements 

 of the bundle become distorted and irregularly placed; and the 

 epidermal system of the leaf entirely disappears, its place being 

 taken by layers of cork-cells covered over by a thin layer of dead 

 shrivelled cells. 



The aecial phases appear on the leaves, petioles, twigs and fruits 

 of their hosts. Occurrence of the aecia on the leaf blades is usually 

 accompanied by an increased thickness caused by a multiplication 

 of the cells of the spongy parenchyma and the frequent arrange- 

 ment of the upper ones into palisade-like layers. Fentzling (1892) 

 in examining pear leaves attacked by G. Sabinae reported a radial 

 elongation of the cells of the spongy parenchyma and a partial 

 formation of cork. On the other hand Wakker (1892) in an in- 

 vestigation of the twigs of Crataegus infected with G. clavariae- 

 forme reported that the formation of cork was inhibited, as well 

 as collenchyma, sclerenchyma and chlorophyll. He also found 

 that lignification of the cells of the medullary rays is interfered 

 with, that activity of the intrafascicular cambium is suspended at 

 a very early stage and that interfascicular cambium is not formed. 

 Starch is stored in large quantities in the hypertrophied regions. 

 Some investigators report an increased deposit of calcium oxalate 

 while others find that its formation is diminished. The aecia 

 occurring on some of the smaller fruits, as those of Crataegus and 

 Amelanchier often occupy the whole of the surface of the fruit. 

 In this case the ovules become completely blighted, the production 



