If normal individuals of a species are tested for the func- 

 tional efficiency of all their parts and then those composed 

 partiaUy Qt entirely of pathological tissue, it will be found 

 that individuals normally constructed attain a maximum of func- 

 tional efficiency, while that of the others remains more or less 

 helow this maximum, no matter what may be the nature of their ' 

 14) variation from the normal histology. Conditions are different, 

 however, if we consider the life history and histology of the 

 cells and tissue instead of their functional efficiency. Cases 

 may be found where individuals constructed abnormally may' surpass 

 ^B well as fall short of the normally developed examples, so far 

 as the hilmber, size, and internal structure of their individual 

 elements are concerned. The normal course of development takes, 

 so to Speak i a gbldeii mean from which it can deviate more or less 

 widely in either direction. Proportions of size, number, etc. 

 characteristic for normal tissue , furnish a standard for the fluc- 

 tuating values to be measured in plants differently diseased. 



It is thus evident that a division of the material into two 

 principal groups is advisable for the histological considerations 

 of the subsequent "general pathological plant anatomy": 



1. The number, size or differ entiation o f the c ells of path- 

 ological tissues .remains more or less be lo w th e n"ormal' . There- 

 fore in one or more ways, the tissues remain in a stage of incom- 

 plete development. We designate as Hypoplasia those abnormal 

 processes of formation which - compared with the corresponding 

 normal processes of development - appear retarded as it were and 

 end prematurely. 



2. The pathological cells and tissues exceed the co nditions 

 of differentiation and growth characteristic of normal individ - 

 uals „ The diversity of forms found to arise through such pro- 

 cess'es of differentiation and growth necessitates a subdivision 

 into several independent groups* 



a. In the simplest case, the abnormal cells differ from nor- 

 mal ones only in their internal structure in the nature of their 

 contents, the character of their membranes, etc. We use the 

 term Metaplasia for the processes of differentiation, by which 

 the cells of any tissue supplement their normal qualities or ex- 

 change them for new ones. 



b. In other cases, the abnormal cells differ from normal 

 ©nes in size . Abnormal increase in cell size we term Hyper - 

 trophy . It is not fundamentally important whether the histology 

 of the cells concerned remains similar to that of normal one's 



er is changed in some way, 



c. If cell division follows cell growth we speak of Hyper - 

 ;plasia . The number of abnormal formations which comes into exis- 

 tence through hsnperplasia is extraordinarily large, and the his- 

 tological composition of the newly produced tissue is exceeding- 

 ly varied, ' later we will have to undertake a further division 

 of this great group. 



Finally there are still to be considered. 



3. The Restitution Processes, After injury and mutilation 

 of the plant body, the injured living part of—ten reacts in such 

 a way, that the lost "part is formed anew. If the structures 

 arising after mutilation resemble those lost, we speak of 

 restitution . Although the tissues thus produced possess, there- 



(5) fore, qualities of the normal ones, they may nevertheless be in- 

 cluded in pathological anatomy, since the formation of the regene- 

 erated tissues, like that of many pathological tissues, requires 

 an outlay of energy and material which is saved to the plant de- 

 veloping im^n undisturbed manner. On account of the correspon- 

 dence fe&«^^n normal and regenerated tissues, the latter must be 

 the first division of this work. 



