ORR—LEAF GLANDS OF DioSCoRBA MACROURA. 65 
themselves, the products of a tissue that is epidermal in origin, 
the chief point of difference between the two being, that while 
the former are temporary structures, the latter become per- 
manent constituents of the glandular tissue of the acumen. It 
is not unreasonable to assume, therefore, that the secretory 
filaments of the gland are merely persistent epidermal scales, 
which have been retained, and modified, for a definite physio- 
logical purpose. 
Attempts to determine the chemical composition of the fluid 
content of the gland cavity were rendered difficult by the 
presence of the micro-organism, and to its influence, no doubt, 
may be attributed some of the unexpected results obtainell. 
At no time was there any visible exudation of fluid from the 
external orifice of the duct, and chemical tests had therefore to 
be applied directly to sections of the acumen, by immersing them 
in a small quantity of the reagent, on a slide, or in a test tube. 
In this way, a study of the biochemistry of the secretory organs, 
and associated tissues, was accomplished, the results obtained 
being briefly collated below. 
Fairly thick sections were treated with Fehlirg’s solution, 
alone, and with the addition of an acid, and were then heated, 
the process being conducted on a slide in the manner recom- 
mended by Schimper, but with purely negative results. 
Barfoed’s solution likewise produced no visible reaction in the 
tissue of the gland, or its secretion. This failure to detect the 
presence of sugar, in some form or other, was unexpected, 
although Correns remarks that he was unable to find either 
sugar or starch in the developing extra-nuptial nectaries of those 
species of Dioscorea, that he investigated. In the present case, 
starch was located in the cells of the mesophyll, but it was 
entirely absent from the glands which were coloured a bright 
reddish-brown by iodine, suggesting the presence of proteids. 
The application of the standard tests for the recognition of 
proteids produced somewhat surprising results. When sections 
were placed in a drop of Millon’s reagent on a slide, and heated, 
a dense brick-red precipitate appeared within the glands. 
Treated in the same way with hot nitric acid and ammonia, the 
glands responded at once to the xanthoproteic reaction. They 
were coloured red by the so-called Raspail’s reagent, and were 
turned to a violet colour by the more delicate biuret reaction. 
The glands were the only parts of the acumen affected by these 
reagents, and, while it is recognised that the successful appli- 
cation of any one of these tests does not in itself afford conclusive 
proof of the presence of proteids, yet, taken together, the 
combined results are undoubtedly indicative of the gland content 
_ being of an albuminoid nature. 
