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larger, unclosed wounds on the Ijranches. In the same way, we find them 

 occurring in specially young peach branches, of which the bark has been 

 greatly injured by bruising or rubbing. 



In my experiments, in wdiich all the eyes were removed in the spring 

 from a considerable number of cherry trees, an exudation of gum occurred 

 with very few exceptions. In other experiments, in which the trunks had 

 been peeled for a considerable distance, gummosis appeared in the bark near 

 the upper girdling cuts, in which no new structures in the forms of callus 

 had been formed. Finally, it is well known that great injury to the roots, 

 or crown, in transplanting, as well as poor grafting, can give rise to the 

 formation of gum. 



All these injuries, in my opinion, do not act through necrobiosis but 

 because of a simple wound stimulus which causes an excessive current of 

 constructive materials to a spot where they cannot find normal utilization. 

 There sets in at the same time, a hastened, new formation of cells, which 

 becomes evident in the formation of the primordia of parenchymatous ele- 

 ments instead of prosenchymatous cells, as in all other processes of wound 

 healing. Therefore, the activity of the new cell formation becomes excess- 

 ively favored at a time when the constructive enzymes already prevail and 

 wall-thickening as well as a deposition of reserve substances should begin. 

 This prevalence of the enzymes of the youthful condition leads to the lique- 

 faction of the diversely formed tissue groups. Such a displacement of the 

 enzyme activity may be considered, in its effect, to be like a wave which 

 continues to advance in the tree until it is stopped by some other constructive 

 force. According to practical experience, such a halt is called by all those 

 factors which condition a normal ripening of the wood and a precipitation, 

 at the right time, of abundant quantities of reserve substances; porous soils, 

 sunny open places, and a supply of calcium, avoidance of over-abundant 

 nitrogen fertilization. 



In treating wounds v/hich are exuding gum, the use of vinegar made 

 from wine is warmly recommended on all sides. I have had no personal 

 experience with it. 



Exudation of Gum in Other Plants. 



Exudation of Gum in the Acacia. 



Moller^ maintains that the formation of Acacia gum depends upon 

 changes similar to those of the cherry gum. He says very generally that the 

 gum of the Acacia is always produced by a transformation of the cell wall, 

 advancing from the outside inward. The walls of the parenchyma cells and 

 the sieve tubes are the first ones to fall victim to the dissolution. (The 

 collapsed sieve tubes form Wigand's Horn prosenchyma.) MoUer observed 

 the gum also as a product of the bark and found that it differs according to 

 the zone in which it is produced. Gum arable is produced by the dissolving 



1 Moller, tJber die Entstehung- des Acacien-Gummi. SitzungsVjer. d. Akad. d. 

 Wissenschaften. Wein. 1875, June issue. 



