70f^ 



We jjc't tlic host insi.Ljht into tlu- nature of the disease by considering 

 the young gummed lateral cherry branch illustrated in L'ig. 155. i and 2. 

 Isolated ducts are shown, first of all, in the middle of the normal wood, 

 which are entirely filled with gum (Fig. 155 2a). This gum has been 

 formed in part from the secondary membranes of the ducts. When treated 

 with hydrochloric acid, whicli colors the walls of the wood cells and ducts a 

 brilliant carmine, as well as the bast fibre cells, the breaking down of the still 

 red wall of the duct into yellow gum, found licrc in drops, may be easily 

 recognized. This phenomenon is fre(iuently only a forerunner, or accom- 

 {laniment of a mucli more extinsi\e formation of gimi, whereby large gum 

 centres are produced in tlie wood and in the bark. 



Even in one year old branches, it is possible to discover the first traces 

 of the gummy exudation liy examining closely cross-sections of young 

 branches in which gummosis is recognizable to the naked eye only in the 

 occurrence of extremely small black points. Ligliter colored places appear 

 at times in the wood body which, with more thorough investigation, are 

 found to be composed of parenchymatous instead of prosenchymatous cells. 

 This abnormal wood parenchyma (Fig. 155 ^ />.) is usually enclosed by 

 normal wood, which separates it also from the cambium (2c). As a rule, 

 these lighter colored places, which are usually deposited side by side, parallel 

 to the periphery, and usually se])arated by thin radial stripes of normal 

 wood, are found in dilTercnt dcNcIopmental stages. Some are i)erfectly 

 unimpaired; others show cells near the centre which have already changed 

 to gum. ]n the same cases, all the abnormal parenchyma and, in the same 

 way, the normal wood, are entirely changed to gum (Fig. 155 2d). In this, 

 the intercellular substances are dissolved first of all; then follow the i)ri- 

 mary, and finally the secondary membranes of the ducts and the wood cells. 

 In such large gum holes, a peculiar process of growth of some cells sets in, 

 together with the simultaneous dissolution of the remainder. While the 

 wood cells and ducts especially undergo gummosis, some medullary ray cells 

 at first grow longer. The starch which they contain is dissolved ; in a few, 

 two new cells may be observed, which elongate in different directions. The 

 medullary ray cells, lying more toward tin- centre and somewhat removed 

 from the gum centre, round oiT and sometimes elongate. In this way arise 

 many celled filaments, v^hich remind one of certain algae (Trentepohlia) 

 (^'ig- 155 "0 ^^^ which grow freely into the gurrimy mass. They are 

 also dissolved, beginning at the outside, but this does not take ])]ace in any 

 definite order. Often the cells at the tip of the filament are found dissolved, 

 with the exception of a thin remnant of the walls. In other cases the cells 

 at the base are dissolved and then the piece of the filament, which has becf)me 

 free, lies isolated in the gummy mass. 



Very similar j)rocesses are found in the l)ark, the thin walled bast cells 

 of which (Fig. 155 h) very easily succumb to gummosis. The gum centres 

 are met with much more frequently in the bark than in the wood. In rare 



