254 The Ohio Journal of Science [Vol. XVI, No. 7, 



Callus was not grown and examined, since from much 

 previous work it is evident that this type of homogeneous 

 tissue, approximately the same for all plants, has no significance 

 in relation to the gall problem. 



Wound wood, however, was investigated, but nothing 

 different was found from similar kinds of tissue reported in 

 other trees. In none of the galls studied was anything found 

 approximating in the slightest degree the condition of things 

 characterizing wound wood. Such may be the case, however, 

 as is shown by Stewart (31) in the gall of Andricus punctatus 

 Bass, on the oak. 



DESCRIPTION OF ZOOCECIDIA. 



Thomas (32) has defined a gall as "a variation in the form 

 of plants caused by a parasite." This definition, though 

 rather widely accepted, is too indefinite and does not delimit 

 certain irregular conditions in plants brought about through 

 predaceous insects and intracellular fungi, conditions which 

 are never associated with the word cecidium or gall. In the 

 author's work on zoocecidia (nematode, mite and insect galls) 

 he has found it possible to adhere to the following definition 

 for zoocecidium: An hypertrophy (abnormal enlargement 

 of single cells) or hyperplasia (abnormal proliferation of cells) 

 of plant cells causally related to certain parasitic animals. 

 Both hypertrophy and hyperplasia may go on in the same gall. 

 The only cases which this definition does not cover are those 

 in which the normal tissue suffers differentiation inhibition 

 without evident hyperplasia or hypertrophy. These cases are 

 extremely rare. The xylem region of gall 1, described in the 

 present paper is an instance of this kind, but as the cortex 

 suffers marked hyperplasia this case is not a true example. 

 Cases of this sort in which the number and size of the elements 

 is not increased, only their qualities have changed, are included 

 by Kiister (15) under "Metaplasias." 



Kiister (15, IG) in his Pathologische Pflanzenanatomie 

 has given phytopathology an excellent classification of cecidia 

 in general. All of the galls described in the present paper fall 

 under his "Heteroplastic Tissues," that sub-division of hyper- 

 plasias which shows "definite quantitative increase of an 

 organ, in which by abnormal cell division, tissues are produced, 

 the single elements of which do not resemble normal ones. 



