CHAPTER XXIX 

 PATHOLOGIC PLANT ANATOMY 



With the multiplicity of higher plant forms, in which the same end 

 is attained in a diversity of ways, the terms normal and abnormal 

 become in one sense merely relative terms for what apparently is the 

 normal method of procedure in one group of plants, may be decidedly 

 different, or abnormal, in other uncommon groups. The words normal 

 and abnormal are, therefore, variable terms, but useful ones. Speci- 

 fically, when we use the word abnormal, we mean the departure, or 

 deviation, from the normal (average) structure or function of the mem- 

 bers of any group selected for investigation. Pathologic plant anatomy, 

 therefore, has to deal with abnormal, but not necessarily diseased 

 organs, and yet a study of diseased tissues is an important subject of 

 investigation for the plant pathologist. 



The material which forms the substance of our inquiry naturally 

 falls into two principal groups. 



1. The differentiation, number or size of the cells of pathologic 

 tissues remain more or less below the normal, so that the tissues in one 

 or more ways remain in a stage of incomplete development. The term 

 Hypoplasia designates those abnormal processes of formation, which 

 compared with the corresponding normal processes of development 

 appear retarded as it were and prematurely. 



2. The pathologic cells and tissues exceed the conditions of differen- 

 tiation and growth characteristic of normal plants, so that a treatment 

 of such necessitates a consideration of several independent groups. 



(a) The abnormal cells differ from the normal ones only in their 

 internal structure (contents, mechanics, etc.) and for the processes of 

 differentiation by which the tissue cells supplement their normal 

 qualities, or exchange them for new ones, the term Metaplasia is 

 used. 



(6) The increase in size of abnormal cells over normal ones is 

 termed Hypertrophy (v-rrep = over, excessive; rpepoi = to nourish), 

 and it is not important fundamentally whether the histologic structure 



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