7oS 



of the inner bark while a less soluble form, similar to the cherry gum, occurs 

 in the middle bark. This may well depend on the age of the affected tissue'. 



As one of the causes which give rise to the exudation of Senegal gum 

 from Acacia Vcrek, Martins'- mentions the action of dry desert winds which 

 blow in the autumn and winter and cause the rupturing of the outer bark of 

 the Acacia, which has become more furrowed because of the August and 

 September winds. Other wounds, which result in the exudation of gum, 

 are caused by a parasite which Martins calls Loranthus scnegalensis. 

 Cryptogamic parasites are also able to cause the wounds to remain open 

 permanently and they thus exercise a stimulus for gum formation. 

 Coryneum gummiparum Oud., which Oudemans observed as bud form of 

 Pleospora gummipara Oud., acts just as Coryneum Beijerinckii does with 

 the Amygdalaceae. 



Gummy Exudation of the Bitter Orange^. 



Italian plantations of bitter oranges (Citrus vulgaris), lemons (Citrus 

 limonum), and sweet orange trees (Citrus Aurantium) have suffered for 

 many years from a disease which is constantly spreading, the ''Mai dclla 

 gamma" of the Italians, which causes such injuries that, according to 

 Novellis*, the Italian Department of Agriculture and Commerce has offered 

 for years a premium of 25,000 lires for a proved means of curing it. 



The disease begins with the appearance of black specks in the bark of 

 the trunk and branches, especially near the points of bifurcation. These 

 spots increase rapidly in size, until, after a little time, they become black 

 places in the bark and split open A yellowish white liquid exudes from the 

 surface, which gradually becomes denser in consistency and stickier, and 

 finally hardens into yellow beads, or glaze-like coatings. The wood under 

 the opening in the bark is brown and in a process of gummosis. If the 

 gum is washed by rain on to other parts of the tree, new centres of disease 

 are said to be produced. We find similar conditions also in regard to the 

 acacia gum and it is not at all impossible that such cases exist. Like the 

 mosaic disease of the tobacco, this may be explained as follows : The 

 enzymatic bodies causing the formation of gum give the impetus for similar 

 changes in predisposed healthy specimens and spread further like a wave. 



1 For the difCeront relations of" cellulose and g-ums to each other in different 

 mucilaginous exudations, compare ToUens and Kirchncr, Untersuchung:en liber den 

 rflanzenschleim; cit. Bicdcrmann's Centralbl. 1S75, II, p. 28. In regard to the forma- 

 tion of the sugar known as Galactose, from mucilaginous giuns, soluble in water, 

 when treated with dilute acid, see Gireaud, Etude comparative des gommes et des 

 mucilages. Compt. rend. T.XXX, p. 477. Peter Claessen, tjber Arabinose; cit. 

 .lahresber. f. Agrikulturchemie, 18S1, p. 88. 



- Martins, Sur un mode particulier d' excretion do la gomme arabique produite 

 par 1' Acacia Verek du Senegal. Compt. rend. 1875, I, p. 607. Killani, tJber arabisches 

 Gummi. Berl. chem. Ges. cit. .lahre.sber. f. Agrikulturchemie 1882, p. 88. 



3 Savastano, L. Note dl patologia arboi-ea. Napoli 1907. The work contains 

 various contributions on gummosis which we imfortunately cannot make use of at 

 present and can only mention as in the last proof sheets. 



4 Novellis, Ettore de, II male della gomma degli agrumi; cit. Bot. Centralblatt 

 1880, p. 469. 



