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is the case when the trees are in sap, thus in February or March at temperatures 

 above 20 C. and below 33 C. The experiment succeeds best with cut branches in 

 the laboratory. When the wounds are made in the open air in that season no gum- 

 mosis ensues, the temperature then being too low 1 ). In summer the cambium of the 

 still longitudinally growing part of young green branches may be caused to form 

 gum by punctures or incisions,_ but these wounds heal quickly, except when kept 

 open by Coryneum or other parasites. 



As to thicker branches, wounded in spring, the microscope show's the following. 



Around the wound a great number of gum canals are formed in -the cambium, 

 about parallel with the axis of the branch, some centimeters long, which become the 

 thinner and shorter as they are more remote from the wound. The canals are 

 separated by the medullary rays, which are with more difficulty converted into gum 

 than the phloeoterma. All the gum canals together form a kind of network, whose 

 meshes are filled by the medullary rays. The whole network has the shape of an 

 ellipse, the gum ellipse*, the wound lies in the lower focus towards the base of the 

 branch. The stimulus extends over the ellipse, evidently farthest in the direction 

 of the branch, less far towards the base and sideways. So it may also be said that 

 the wound stimulus extends farthest opposite to the descending current of nutrient 

 matter, following the phloem bundles, or along wih the ascending water-current, 

 following the wood. Evidently the gum canals are more easily formed in the better 

 fed cells above the wound than in those beneath it, where the nutrition must be 

 worse. This is especially obvious in ringed branches. Wounds in the cambium, 

 directly above the ring produce much more gum than those immediately below 2 }. 



Under ordinary circumstances the branches, after simple mechanical wounding, 

 are soon completely healed, and if the cambium at the outside of the gum canals then 

 again begins to produce normal secondary wood, the gum canals may later be found 

 back in the wood itself 3 ). Evidently the healing takes place as soon as the stimulus 

 ceases, and so it is not strange that when it continues by poisons or parasitism the 

 gum production also continues. 



Parasitism as cause of gummosis. 

 The connection between wounding aud parasitism. 



Wounds in peach branches treated with poisonous substances, such as sublimate, 

 produce gum much longer and more copiously than the like wounds without sublimate. 



l ) If the wounds are infected with Coryneum, an extremely copious gum production 

 follows in spring, as the parasite then finds abundant food in the branches. There is, 

 however, no season when wounds, infected with Coryneum, do not sooner or later 

 yield gum. 



) The nature of the power, by which the food transmitting, descending sap 

 current moves through the phloem bundles, is not known. It is thus not impossible, 

 that if the cause of gummosis is of a material* nature, a lysine, moving through the 

 tissues, it is able to run in opposition to the descending current. I think, however, 

 that the extension of the stimulus does not go along the phloem but along the xylem 

 bundles and the young wood, with the ascending sap. 



8 ) I have never seen distinct gum canals in the secondary wood, but according 

 to the descriptions they occur eventually. 



