of unfluences. or tissues functionally efficient undergo subse- 

 quent changes. In this latter case they lose wholly or in part 

 their aoility to function, or new tissues are produced on the 

 plant body of such a nafure that the diseased and deformed or- 

 gans either do not serve the organism as a whole, or at least 

 less than those termed normal. AccCrdingly, the following tis- 

 sues among others may be considered as pathological;- the color- 

 less mesophyll of etiolated leaves which through l&ck of light 

 is kept from developing into functionally efficient tissues, and 

 the assimilatory tissue whose ohloroplats degenerate under the 

 influence of external factors, thus rendering the cells incap- 

 able of assimilation, i^arther, new formations like galls', are 

 to be designated as pathological. Their tissues do not serve 

 the organism as a whole, and not infrequently considerable quan- 

 tities of nutritive material are lost to the organism through 

 their formation. To pathological tissues may be added also 

 wound cork, formed after injury, and "callus" tissue, although 

 the first, by closing the wound, protects the functional effi- 

 jgiency of the organism as a whole, and the second, by a new for- 

 mation of roots and shoots, has the power of regenerating the 

 original size and efficiency of the mutilated plant body. In 

 (3) both cases tissues are concerned in whose formation not so much 

 is accomplished for the organism as a whole, as under normal con- 

 ditions, thait is, as would have been produced by the normal tis- 

 sues of the organism of its integrity had not been destroyed. 



Emphasis of the functional characters by which abnormal 

 cells and tissues are distinguished makes possible the rough 

 limitation of the field of our work. Any sharp distinction be- 

 tween the pathological and the normal cannot, however, be car- 

 ried throTigh in this way. In many cases, the difficulty of 'judg- 

 ing with certainty of the physiological values of the different 

 tissues would prevent this. A microscopical investigation of 

 their structure does not always enable one to decide as to their 

 physiological significance, and often for technical reasons, the 

 tissues in doubtful cases, are not accessible for experimental 

 investigation. In listing definite tissue forms under any one y 

 of our chapters, we must be guided by histology and etiology as 

 well as by analogous cases. However, I hope we will not need to 

 deviate from the path indicated by the physiological point of 

 view emphasized above. 



The valuation of cells and tissues according to their physi- 

 ological efficiency reveals the characteristics common to all 

 pathological tissues. When forming groups and sub-groups within 

 the field of our work, it will be advisable to consider ontogen- 

 etic and histological points of view as the most important. 

 Therefore, we will unite pathological tissues of similar life 

 history and similar histology and discuss them in independent 

 group's. 



Various principles of classification are open to us, we may 

 either describe successively, the individual tissue forms and 

 organs of the plants, and the many variations from the normal 

 structure found in them under certain conditions or we may anal- 

 yse processes of growth, maturation and differentiation through 

 which abnormal cells and tissues arise, and unite them into in- 

 dependent groups produced by similar processes, without consid- 

 ering which tissue appears changed pathologically, or wha-t or- 

 gans are involved. In the first case a specialized pathological 

 anatomy would result, in the other case a general one. Since we 

 will have to take into consideration, plants of the most widely 

 different SQrts, one-celled as well as many-celled, thallophytes 

 as well as tsormophytes, it seems advantageous to me to arrange 

 our material from the ^oint ©f view of general pathological 

 anatomy . In the concluding chapter there will be opportunity 

 ■fn-r- fUrestcTtilns in ouriline, a special anatomy, at least for the 



