424 Mas see . — The ‘ Spot ’ Disease of Orchids. 
the accumulation of methylene blue by tannin-bearing cells, 
as pointed out by Pfeffer 1 , held good, the vesicles becoming 
stained deep blue after remaining in an exceedingly dilute 
aqueous solution of methylene blue for twenty-four hours ; 
iodine-green may be substituted for methylene blue with 
good results. All the above reactions are most decided before 
vacuolation takes place ; in fact, when the vesicles are fully 
distended, but little colouration is produced by any of the 
reagents mentioned. On the other hand, the presence of 
proteids in the spheres is suggested by the rapid staining of 
the mass, on the application of such reagents as eosin, car- 
mine, iodine, &c. Carbohydrates are also in all probability 
present. 
The spheres originate in the cell-sap, and their presence 
depends entirely on plasmolysis of the cells, which occurs 
during the earliest phase of the disease. 
Contemporaneously with the formation of the tannin- 
vesicles the cytoplasm becomes turbid, the primordial utricle 
at the same time becoming tinged brown, and undergoing 
important changes. In some cases the inner surface of the 
latter becomes uniformly covered with minute, spherical 
masses, and in this condition resembles, superficially, cells 
filled with the spores of a Plasmodiophora ; here, however, the 
resemblance ends, as the minute spheres are found to form 
only a single layer lining the primordial utricle, and not com- 
pletely filling the cell, as in Plasmodiophora ; furthermore, 
reagents show that the spheres consist of tannin, and not 
protoplasm (Fig. 7 b). In other cases the inside of the epi- 
plasm, and sometimes also the cell-wall — which, along with 
the other parts, undergoes disintegration-— is covered with 
tubes or variously branched, very slender rods of a brown 
colour. Usually, however, the epiplasm or primordial utricle 
becomes entirely disorganized, drops of tannin accumulate at 
various points in its substance, accompanied in many instances 
by minute crystal-like bodies. These eventually disappear, 
1 Ueber Aufnahme von Anilinfarben in lebenden Zellen, Unters. a. d. bot. 
Instit. zu Tubingen, Bd. II, p. 179. 
