392 BOTANICAL GAZETTE [DECEMBER 
and potassium iodid-iodin proved to be by far the most satis- 
factory reagent for the demonstration of callus. The two con- 
stituents of this reagent were prepared fresh, and then mixed in 
different proportions until one giving the best results was 
obtained. The proportions vary with the different kinds of 
plants tested. In using this stain, though the presence of the 
celloidin is not a serious objection, it is preferable to dissolve 
out the celloidin, wash in alcohol, then in distilled water, and 
examine in stain on the slide. 
In face view it is difficult to make observations on account 
of the “globules brillants,” hence the most reliable observa- 
tions can be made on sectioned plates. Almost at once after 
applying the stain, the callus plugs become evident, staining a 
dark red-brown (fig. 7). They appear as more or less fine rods, 
completely traversing the sieve plate, and their number ina sieve 
plate depends on its size. The cellulose is slower in staining; 
at first it is light blue or a violet, and later a deep blue. Hence 
the callus plugs are to be seen most clearly in the early stages 
of the staining process. The stain unfortunately is not perma- 
nent. Callus was clearly demonstrated in the species under 
investigation, but on account of the size of the cells and of the 
sieve plates, 7. darbara proved the best subject for the purpose. 
As one of the characters of the sieve tubes of the Osmundaceae, 
we record, therefore, the regular occurrence of callus plugs in 
the sieve plates. 
The “globules brillants” are exceedingly abundant in the 
sieve tubes, and especially in the older ones (fig. 7). While 
they adhere to the protoplasm of the cell and may be found in 
any part of the cell they are by far most abundant about the 
sieve plates, dotting their surface, filling the pits, and surround- 
ing the entrance to the pits. They are evidently not homoge- 
neous, but appear to consist of two substances, one of which is 
more refractive than the other, for by slight focusing up and 
down they change from a dark looking, opaque granule to a light 
semi-translucent spherule. Jodin solutions stain them brown, 
not appreciably different from the callus plugs. Occasionally 
