166 PLANT ANATOMY. 
Beijerinck' attributes the origin of gum arabic, the “ gum- 
mosis ” of species of Acacia of Africa, to the fungus Pleospora 
gummipara Oudemans; another fungus, Corynewm Beijerinckit 
Oudem., causes the gummosis of the Amygdalex. Frank does 
not concur in this view, and Wiesner (Botan. Zeit., 1885, p. 577, 
also Ber. d. Deutsch Chem. Ges., 1885. Referate p. 639), recently 
attempted to show that the transformation of cellulose (and 
starch) into gum or mucilage is due to a peculiar ferment, a 
“diastatic enzyme.” At all events, the true gummosis, which is 
certainly a pathological process, must be separated from the 
gum formation which serves as a protection to tissues (see sub- 
sequent references), and which is only intelligible from a physio- 
logical point of view. They are also distinguished from each 
other by the fact that the ‘‘ pathological gum ”—and only this 
is of interest to us here—is formed through a metamorphosis of 
the membrane, while the ‘‘ physiological gum” represents an 
exudation of the membranes into the cell-cavities. 
The transformation of cellulose into gum and mucilage can 
also take place without so great an alteration of the cells and 
tissues as in the case with gum arabic and tragacanth. In such 
a case only one layer of the membrane becomes metamorphosed, 
as is shown, for instance, by the conversion into mucilage of 
the filamentous Alge. The gum mucilage of the glandular 
hair (colleters) or many foliage buds, which is often mixed with 
volatile oil and resin, is formed through the conversion into 
mucilage of a membranous layer (collagen layer *) lying under- 
neath the cuticle of the glandular hair. The mucilage of quince 
seed and of flaxseed is probably also formed primarily through 
a conversion into mucilage of only the secondary membrane of 
the epidermis cells* of the respective seeds (Frank). The 
seeds of many of the Papilionacesx, for instance, those of T’rigo- 
'* Onderzoekingen over de Besmettelijkheid der Gomziekte bij 
planten.” Amsterdam, Joh. Miller, 1884, 4to, 46 pages, 2 plates. 
* KcAla@ glue, and yevvae to produce, Hanstein, ‘‘ Ueber die Organe 
der Harz- und Schleimabsonderung in den Laubknospen.” Bot. Zeit., 
1868, No. 43, 
: * Berg’s ‘‘ Atlas,” Plate XLVI., Figs. 122, 128 6. 
