447 



From the examples already cited it is evident that the intumescences 

 may occur on all aerial organs of plants. They form one link in a chain of 

 phenomena which in part commonly occur together and in part, in fact, 

 overlap. We have described the simplest disturbances as "Aurigo ;" they 

 are characterized by the impoverishment of some tissue groups in the 

 interior of the leaf with a destruction of the chlorophyll apparatus, usually 

 with the formation of carotin. As the chlorophyll disappears the cells are 

 apt to become distended. They fill the intercellular spaces, thus exercising 

 pressure on the surroundings ; they finally die as the cell walls become 

 suberized. Such nests of over-elongated cells are also termed "internal 

 intumescences." In real intumescences the processes of impoverishment 

 and cell elongation begin in the peripheral layers of the organs and in fact 

 usually in the sub-epidermal 

 cell layers, more rarely in 

 the epidermis itself. The 

 process of over-elongation 

 is less impeded here and 

 frequently advances into 

 the more deeply lying tis- 

 sue layers, so that we find 

 cases of intumescences be- 

 ginning on the under side 

 of the leaf and gradually 

 including the whole meso- 

 phyll as far as the upper 

 epidermis. If the forma- 

 tion of cork sets in in the 

 intumescence tissue, we find 

 wart-like or pitted cork 

 centres which can lead to 

 the complete perforation of the leaf. 



On the trunk the intumescence manifests itself in the hypertrophy of 

 the bark parenchyma which, in isolated enclosed centres, breaks out from 

 the bark in the form of warts with a smooth or repeatedly split outer sur- 

 face. If the processes of over-elongation are not restricted to small isolated 

 centres but attack the parenchymatous tissue in large, connected surfaces, all 

 the organs rupture, causing the condition which we have called "dropsy." 



Although the phenomena described here are related structurally, we 

 have treated them separately because dififerent conditions are the dominat- 

 ing causes of dififerent outbreaks. Many investigations have shown that an 

 atmosphere heavily ladened with moisture is a decisive influence in causing 

 intumescences. 



'J^eferences to my work and that of other older investigators may be 

 found in the bibliography of Kiister's^ "Pathological Anatomy." I will cite 



Fig. 



86. Cross-section through the outer surface of 

 pea-pods with intumescences. (Orig-.) 



1 Kvister, Ernst, Pathologische Anatomie. Jena 1903. Gustav Fischer. 



