36 HISTORY OF PHYTOPATHOLOGY 



He believes diseases to be conditions brought about 

 through internal disorganization of the nutrition proc- 

 esses; that they have their origin in a lack of certain 

 chemical constituents of the sap. He observed, however, 

 that "entophytes," the fungi, protrude their structures 

 from the stomates of the diseased plant (see his sketches) 

 and concludes that they must be the transformed sap 

 of diseased tissues. His theory is that this morbid sap 

 exuded into the substomatal cavities and intercellular 

 spaces is converted, under the influence of the still living 

 cells of the host, into fungous structures, i. e., conidio- 

 phores and spores. Of mycelium he seems to have had 

 no true conception, as may readily be gathered from 

 his drawings of cross-sections of diseased leaves. The 

 theory of spontaneous generation, generally accepted by 

 the scientific men of his time, was also for Unger a fun- 

 damental conception, hence his idea of the relation 

 of pathogene to host was but a natural and logical 

 deduction. Nevertheless, mycologists of the period 

 were collecting and studying fungi, observing the char- 

 acter of their spores and their manner of germination. 

 Some were even contending that the entophytic forms 

 were entirely distinct from their host plants. Their 

 observations and deductions were not to materially in- 

 fluence during the Ungerian period the generally accepted 

 explanation of the relation of the fungus to the plant on 

 which it grew. Their work and their ideas were, however, 

 to profoundly affect the phytopathologic thought of the 

 next period, as we shall see. 



Unger dominated the phytopathologic thought of his 

 time, as is strikingly shown in the work of Arend Joachim 

 Friedrich Wiegmann, whose book on "The diseases and 



