34 



CAUSE AND NATURE OF CKOWN-GALL 



or on a seedling in water culture, so that the light has access to 

 it, after a time it changes to light green from the development 

 of chlorophyl in some of its outer cells. Its growth is sur- 

 prisingly rapid. When kept in a water culture for purposes of 

 observation the increase in size can be readily recognized from 

 day to day. In a mouth's time a rapidly developing specimen 

 may grow from a scarcely discernible speck on the side of the 

 root to a body more than a quarter of an inch in diameter. 



At first the gall has a uniforn outer surface, but after a time 

 it becomes somewhat warty from unequal growth. Under ad- 

 verse conditions the growth may be checked for a time, but if 

 this continues the outer portion begins to assume a reddish 

 brown color, which gradually darkens and extends over and 

 through the entire gall. Decay soon sets in and the whole of 

 the hypertrophied tissue falls away or can be readily broken 

 from the root. Early in its life the surface of the gall loses its 

 white appearance and darkens to a reddish brown, probably 

 from the disorganization of the contents of the outer cells and 

 the action of various species of saprophytic fungi upon them. 

 After any portion of a gall has changed color that portion has 

 lost the power for further growth. Specimens are occasionally 

 observed where a new growth begins as clear transparent globu- 

 lar pustules in hundreds of places on the surface of a large gall 

 (Fig. 1 1 ). In such instances the places immediately under the 

 new growths retain their normal whiteness, while the remainder 

 of the surface is discolored to a considerable depth. 



PIG. 12.— The root and stem of an almond seedling, cut longitudinally so as to show 

 the gall attachment. 



