The processes of differentiation and growth thus briefly 

 characterieed lea^ to the formation of the following five 

 chapters. 



I. - Restitution, 

 II. -t Hypoplasia, 

 ni. - Metaplasia, 

 IV, - Hypertrophy, 

 V, - Hjrperpjasia, 



In all cases, with words like hyperplasia, eto» we are con- 

 cerned priimrily with the naming of proceeses. Hyperplasia, for 

 example, is the process leading to the formation of cell out- 

 growths, Howe#er, we Will, in the follo\Ting chapters, take the 

 liberty of designating by the same terms, the actual product of 

 the process of grov-th or division, etc* The cell outgrowth it- 

 self is a hyperplasia,- the abnormally enlarged cell a hyper- 

 trophy and so forth. In this we will follow the example of the 

 physician who in the same way uses both abstractly and concrete- 

 ly the terms here named, 

 J 



The difficulties encountered in defining the whole pro- 

 vince are met again when establishing single groups. In many 

 of these we must give up absolutely sharp boundaries, For in- 

 stance, "hypertrophy and hyperplasia" often merge Into one an- 

 other since, under certain external conditions, in organisms of 

 certain constitution, and in a certain stage of disease, only 

 enlargement of the cells takes place, while in others cell-di- 

 vision may also arise. The few debatable cases in which defin- 

 ite disease-phenomena seem to belojig to one chapter or to the 

 other, should not prevent us, however, from leaving both of the 

 groups named to stand independently side by side. 



At this point, we must call attention to certain limits'^ 

 tions which influence us in the definition of our subject. All 

 pathological structures of cells and tissues should not come 

 under our consideration:- the finer nuclear and protoplasmic 

 structures are excluded first of all. The many results furnish- 

 ed in the past few years by cytological investigation also throw 

 light in part upon abnormal cell and nuclear structures. How- 

 ever, the lack of unity, in judgixjg of normal structural rela- 

 tions, which still prevails even among scientists, seems to 

 prove that the time for a comprehensive consideration of abnor- 

 mal conditions has not yet come. We will rest content by call- 

 ing attention incidentally to changes in nuclear and ptoto- 

 plasmic structures, associated with hypertrophy of the cells or 

 hyperplasia, etc. and in conclusion point out some problems and 

 give some bibliographical citations. The further phenomena of 

 degeneration and dissolution so often noticeable in cytoplasm, 

 (6) nucleus, chromatophores and cell-membrane will be excluded. 

 Some remarks on the phenomena of degeneration may be found in 

 Chapter V.. Finally micro-chemical conditions which vary from 

 the normal and are found in pathological cell and tissue forms 

 will be mentioned only incidentally. Irregular reactions of 

 the cell contents and membranes have more to do with abnormal 

 metabolism of diseased plants, than with their pathological 

 tissue structures, the discussion of which is our sole task. For 

 the rest, compare the concluding remarks in Chapter V. 



Since in forming groups and sub-groups, we v/ill take pains 

 to place the most natural boundaries possible to the separate 

 divisions of our work, we.iBust consider practicably, besides 

 ontogenetic and histological features of pathological plant 

 tissues, still other distinctive ones. Among these, etiologi - 

 cal features are of first importance. In every form of patho- 

 logical development we will inquire for the causes producing it. 

 The influence upon tissue formation of abnormal supply of light, 

 abnormal nutritive conditions, abnormal water supply, and many 

 others, should be investigated. It will be found that abnormal 



