404 GENERAL PLANT PATHOLOGY 



organs, tissues and cells, as expressed in the growth, plasticity and 

 processes of differentiation under the influence of the exciting cause, as 

 is e\-idenced in the formation and nutrition of galls comprehended 

 under the general head of cecidogenesis. 



The recent study of the developmental mechanics of pathologic 

 tissues calls for an investigation of stimuU, and the reaction to stimuli 

 where every reaction presupposes a capacity for reaction and where the 

 cells of different tissues vary in this respect and no cell remains always 

 the same, but changes without any influence of the external world with 

 the age of the cell, as well as the fact that even.- reaction presupposes 

 previous conditions which permit the reaction to take place. Such 

 considerations as these introduce the student to the investigation and 

 terminolog}- of Roux, as set forth in his " Terminologie der Entwick- 

 lungs ^lechanik der Tiere und Pflanzen," 191 2, and to the work of 

 Vochting, Kiister, Klebs, Haberlandt, NSmec and others along experi- 

 mental Unes. Correlation, Neoevolution, Neoepigenesis are terms with 

 which the pathologic student must become acquainted. He learns that 

 Osmomorphosis comprehends all osmotic and turgor influences which 

 determine the forrn and differentiation of cells and tissues; that mechano- 

 morphosis is where plant cells and tissues have been modified in develop- 

 ment by mechanic pressure and puU; that chemomorphosis is where 

 chemic influences are the determining factors in molding the form and 

 controlling the differentiation process; that trophomorphosis is where 

 abnormal nutrition is influential locally in the transformation of plants. 



The consideration of chemomorphosis shows us that we may deal 

 with known chemic bodies the action of which can be studied experimen- 

 tally, or we may be concerned with unknown chemic substances, as the 

 poisons injected into the tissues of a plant by the gall forms which pro- 

 foundly influence the formation of the gall tissues. 



Trophic correlation, or trophomorphosis, exists between the parts of 

 a cell, as well as between the organs of a plant, or the tissues of the 

 organs. The action within the cell may be between the nucleus and the 

 cjrtoplasm, and its importance in pathologic plant anatomy has been 

 experimentally studied by Gerassimoff and Nfimec. Gerassimoff's 

 research dealt with the influence of the size of the nucleus on the cyto- 

 plasm, while N?mec discovered that in chloralized roots of Vkiafaba the 

 cells with normal diploid chromosome content had didiploid and tetra- 

 diploid chromosome-rich nuclei, and that the greater the content of the 



