454 



When examining badly diseased specimens, it is noticed that a number 

 of glassy places occur like warts on the upper surface. The cross-section 

 shows that while the outer part of the bark of this piece of stem is still dark 

 green and normally constructed, the underlying bark layers lack chlorophyll 

 and starch and have greatly enlarged cells which cause the warty excres- 

 cence. In contrast to the usual intumescences in which an elongation of the 

 sub-epidermal layers causes the warty outgrowths which often rupture, I 

 have termed the abnormal enlargement of the cell centres lying deeply 

 depressed in the tissue, "internal intumescences." In this, these phe- 

 nomena are related to the yellow-spotted condition described above. Here 

 the first stages of the disease are found in centres of cells poor in content, 

 browning and turning to cork in the midst of green tissue ; only in cacti the 

 stems are affected, while in I\indanus the changes are found in the leaf. 



The cell aggregations, which usually increase only in one direction, 

 collapse, while, especially in the bark of the cactus, the cells retaining thin, 

 colored walls, are usually elongated into tubes and have a star-like arrange- 

 ment. From these inner diseased tissue centres, the process of impoverish- 

 ment and over-elongation of the bark parenchyma extends backward toward 

 the wood-ring and laterally in the direction of the bark, constantly further 

 around until a considerable part of the stem is browned or blackened. 

 Finally the outermost cell layers are also attacked by the discoloration 

 without the usual appearance of any over-elongation; rather, the stem 

 appears as black as ink, even to the naked eye. 



In the first stages of this disease, while the tissue still has a glassy appear- 

 ance, the process of blackening occurs almost immediately after the sections 

 are made, indicating that even then there are large amounts of tannic acid, 

 which unite with the iron of the knife. Since, however, the discoloration 

 follows when the plants have been injured with a horn knife, or with a 

 platinum spatula, the presence of a sensitive substance must be assumed 

 that rapidly discolors in the presence of the oxygen of the air. But 

 guaiacum tinctures alone, or with hydrogen peroxide, do not give a blue 

 coloration. W'ith litmus paper the whole bark parenchyma gives a sharp 

 acid reaction. 



An accumulation of glucose may be considered as a factor which might 

 begin the over-elongation of the cells ; for, after treating the section with 

 the Trommer sugar test, cuprous ox id is very freely precipitated in the 

 glassy tissue as a whole, and this precipitate is scantier toward the healthy 

 tissue. The proportion of starch content is the reverse. In the most dis- 

 eased tissue, it is nil, while the healthier surrounding tissue displays starch 

 abundantly. The proportion of calcium oxalate is peculiar; it occurs usually 

 abundantly in the slime passages. In healthy green bark tissue, this calcium 

 oxalate occurs chiefly as raphides, while in the diseased parts it is found 

 usually in short octahedrons and at times in large cylinders. Probably 

 var}^ing amounts of the water of crystalization determine the form. 



