7o6 



The oxygen carriers, which form gums, are now actually (Icmonslrahle 

 as enzymes which are produced in the sprouting of the buds and, in fact, are 

 present even before the diastase. The latter will then dissolve the hemi- 

 cellulose, or other gums, as Griiss has proved for tragacanth. 



If such enzymes are produced in excess or their anti-bodies develop in 

 loo small amounts, they hinder the normal development of the cell wall in 

 embryonic cells, or begin the process of liquefaction in the complete cell of 

 the mature wood, so that pathological gum centres are produced. 



It is not at all improbable that an excess of oxalic acid, like the hydro- 

 lyzing sulfuric acid and other mineral acids, acts like the naturally formed 

 ferments and produces thereby an exudation of gum. Such an increase of 

 oxalic acid action can either be brought about by its more abundant forma- 

 tion, or through its lesser combination with calcium. Thus, for example, 

 Mikosch^ calls attention to the fact that almost no calcium oxalate crystals 

 are found in the tissues involved in this transformation. It is evident from 

 Benecke's works- that the content of these crystals depends upon the nutri- 

 tion. He found in his cultures that the addition of nitrates favors the 

 formation of calcium oxalate; that feeding with ammonia decreases this 

 formation. 



Among the parasites producing an exudation of gum, Clasterosporium 

 carpophilum (Lev.) Aderh. (Coryneum Beijerinckii Oud.) should be named 

 first of all. Nevertheless, a certain predisposition of the organ is necessary 

 if the fungus should become effective. Aderhold'' found in his inoculation 

 experiments with leaves that red fungous spots occur without the formation 

 of gums as, conversely, wounds with an abundant formation of gum could be 

 found in the midribs of the leaves and in the cambium of branches in which 

 the fungus was absent. The other parasites behave similarly ; Cytospora leu- 

 costoma; Monilia fructigena and M. cinerea, Botrytis cinerca and many 

 kinds of bacteria*. 



It is very possible that, in some of the parasites here named, oxalic acid 

 is the poison produced by them which causes gummosis. 



Before we take up the question of overcoming exudations of gum, it is 

 necessary to turn our attention to the conditions under which the disease 

 appears. Duhamel's theory is found most frequently confirmed in pomo- 

 logical literature. He thinks that cherry trees, which are planted in too 

 strong soil, are most subject to the disease. We find this proved especially 

 with the peach and cherry if clayey soil is understood by the term "strong 

 soil." Exudations of gum are found less frequently on warm, porous soils 

 wliich can be very rich. Further, we find exudations of gum abounding in 



1 Mikosch, K. Untersuchungren iiber die Entstehung- dcs Kirschgummi. Sitz- 

 ungsber. d. Akad. d. Wiss. Wien; cit. Bot. Contmlbl. 1907, XXVIII, No. 27. 



- Bcnccke, W. tJbcr Oxalsaurebi Idling- in griincn Pflanzen. Bot. Zeit. 1903, Vol. 

 LXI. cit. Bot. Centralbl. (Lotsy) 1903, No. 27, p. 16. 



■^ Aderhold, R. t)bor Clasterosporium carpophilum (LSv.) Aderh. und die 

 Beziehungen desselben zum Gummifluss dcs Steinobstes. Arb. d. Biol. Abt. d. Kals. 

 Gesundheitsamtcs 1902, Vol. II, Part 5. 



4 lluhland, W. tJber Arabinbildung durch Bakterien und deren Beziehung zum 

 Gummi der Amygdalaceen. Ber. d. Deutsch. Bot. Ges. 1906, Part 7. 



