224 BOTANICAL GAZETTE [MARCH 
give the reaction. The lead subacetate precipitate, as also the gelatin and 
hide powder residues, is stained very dark brown by the reagent. 
The method proves very convenient in studying the distribution of 
tannin in fruits and other parts of plants. Tissues which can be distin- 
guished only with difficulty in the unstained hand section become very 
sharply differentiated after treatment with nitrous ether vapor. For 
example, a piece of the woody fruit stem of the date stained in this way 
reveals a very narrow tannin zone near the cuticle, corresponding very 
closely to the more prominent one in the fruit. In thin section this zone 
resolves into rather widely separated, very small, dark-colored cells. A 
large Japanese persimmon weighing one-half pound can be completely 
stained in 24 to 48 hours 
without any abrasion of the 
cuticle. The process offers 
the further advantage that 
the tannin is deposited in 
the cells where it occurs, 
and thus eliminates all 
danger of carrying soluble 
tannin across the face of a 
section. In the date the 
outer tannin-bearing tissue 
Fic. 8.—Deglet Noor date showing shar 
separation of tannin layer from inner flesh after : 
ethyl nitrite treatment. sharply from the inner 
tannin-free tissue after pro- 
longed exposure to ethyl nitrite. In some fruits, certain cells stain violet 
or lilac instead of brown, while others take no stain whatever until after 
prolonged treatment. This is notably true in the wild persimmon, which 
stains brown very readily just beneath the skin and again at the center 
of the fruit, with the exception of occasional cells interspersed through 
the flesh. Further exposure to the vapor of nitrous ether stains all the 
tannin cells uniformly brown. It is not evident whether this phenome- 
non depends entirely on permeability of the cell walls, or whether there 
is an actual difference in chemical composition of the cell contents. _ 
For laboratory use a 20 per cent. alcoholic solution made by diluting 
the 90 per cent. commercial nitrous ether is recommended. Amyl nitrite 
may be used, but is disagreeable to work with. Ordinary sweet spirits 
of niter, which contain about 4 per cent. ethyl nitrite, may be used, but 
will require much longer exposure.—A. E. Vinson, Arizona Agric. Exper- 
Station, Tucson, Arizona. 
. 
