Ö12 



provoked in many Aniygdalaceae, as almond, peachalraond, apricot, 

 peaph, plum, cheiTV, and bird's cberrj. 



But these tliree groups of causes may all be considered from one 

 single point of view, by accepting that gummosis is always the effect 

 of a wound stimulus, proceeding from the slowly dying cells, which 

 are found as well in every wound, as at poisoning and parasitism. 

 These dying cells may change into gum themselves, but besides, exert 

 their influence on cambium tissues to distances of some centimeters. 

 This distance-inlluence is the principal effect of the wound stimulus. 

 But poisoning by sublimate or oxalic acid, introduced under the bark, 

 can as well excite gummosis as an incision or a wound by burning 

 or pricking. Neither the dead cells nor the poison are the active 

 factors here ; the stimulus proceeds from the slowly extinguishing cells, 

 so that gwnmosis is essentially/ a necrohiotic process. Probably the 

 dying cells, after the death of the j)rotoplasm, give off an enzyme 

 or enzyme-like substance, a lysine, fixed during active life, but, which 

 being freed b}' necrobiosis and absorbed by the young division j)roducts 

 of the cambium causes their cytolysis. This reminds of the cytolysines 

 of the animal body, originating ^vhen foreign cells are introduced, 

 which liquefy the corresponding cells, for example the haemoly sines 

 which dissolve the red blood-cells. Furthermore of the bacteriolysines 

 and of cytase, the enzyme of cellulose. 



If the hypothesis of the existence of a "gumlysine" is right, — and 

 I think it is, — this substance must be of a very labile nature, for 

 when bark wounds are infected with gum, quite free from germs 

 of parasites, no more abundant gummosis is observed than at 

 mechanical wounding only. But a difference, however slight, will 

 certainly exist. 



Gummosis produced hy loound stimulus. 



The influence of this cause is best studied in the following experiment. 



A deep wound, penetrating into the cambium of a branch of 

 almond or peach, commonly soon heals completely, but it maj' be 

 tliat gum flows from the wound. This is the case when the trees 

 are in sap. thus in February or March at tempei-atures 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 gummosis ensues, the temperature then being too low. ^j Tn 



^) If the wounds ave infected with Cori/neum, 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. 



