Introduction 1 



(1) We *bharacterize as abnormal all those forms which deviate 

 from a norm. Since a comparative consideration of different 

 kinds of form-groups leadis to the establishment of different 

 kinds of norms, the meaning of the word abnormal will have to vary 

 in accordance with the groups under immediate observation. When 

 studying organisms 7/6 have to establish a norm by comparing rep- 

 resentatives of a species. This norm will differ from that es- 

 tablished in the consideration of greater form-groups. Therefore 

 in speaking of abnormal forms, we will have to define the limita- 

 tion of the form-groups, to accord with the investigation with 

 which we are then occupied. Botanists commonly consider the 

 growth in thickness of the tree-like Liliaceae, many lianes and 



so forth, 9;S abnormal because it differs essentially from the 

 growth in thickness in the other phanerogams. In this case the 

 norm has been deducted from a consideration of all phanerogams. If 

 we find double buttercups or fasciated dandelions in the meadow, 

 and plum pockets, cankers, etc. on fruit trees, we term them ab- 

 normal formations, because a comparative consideration of the in- 

 d.ividuals of similar species leads to the establishment of a norm, 

 characterized by single flowers, simple scapes, trees free from 

 canker and so forth. Abnormalities of this kind are also called 

 pathological phenomena or diseases. In this it is i-ssumed, that 

 the functional efficiency of the "abnormal" organism or organs is, 

 in some way and in varying degrees, below that of ''normal" ones. 



Kot all pathological forms found in the plant kingdom are 

 suited for consideration in the manner proposed, only those cases 

 will be discussed in which cells and tissues of abnormal kinds are 

 formed. The comparative treatment of these cases leads to the 

 founding of a "Pathological Plant Anatomy", the characteristic 

 features of which the author has sought to outline in the present 

 work. , 



(2) Before taking up a detailed consideration to the abundant 

 material furnished by the study of pathological plant tissues, 



we must first decide whether it is possible to formulate an exact 

 definition for the tjoncept of the "pathological", in contradis- 

 tinction to the normal. 



In my opinion, the efforts of earlier authors to define 

 "pathological", when working with plant diseases, have only proved 

 the impossibility of any sharp. division into normal or healthy 

 and abnormal or lathological, ^ nature. This is as impossible 

 as an exact distinction between the plant and the animal kingdoms, 

 Porms -will always be found, of which the frue classification re- 

 mains uncertain. We will not undertake the hopeless task of find- 

 ing an entirely satisfactory definition; the same difficulties 

 exist also for the relatively limited sphere of our anatomical \^ 

 considerations, that are found in the whole province of pathology. 

 We will only inquire which are the characteristics common at 

 least to the majority of the forms which we, in accordance with 

 general usagjg, are to designate as pathological. 



Ko useful result whatever is obtained by taking into consid- 

 eration the histology of abnormal tissues. The anatomical struc- 

 ture of pathological tissues shows the greatest diversity conceiv- 

 able. This will be fully demonstrated later. No features are 

 found in common. Similar conditions exist in considering their 

 etiology, for the most varied of external conditions may cause 

 the formation of pathological tissue. We obtain useful results 

 only when we take into consideration the physiological peculiar- 

 ities of the tissues. All the cases which we can designate as 

 pathological in the plant involve the omission or weakening of 

 some function. Either the tissues are retarded in their func- 

 ■fcianal efficiency: that is in their normal formation by some kind 



