400 
hydrocyanic acid and for saponin (two substances, the taxonomic 
value of which has already been referred to). This choice of plant 
substances may be defended as follows :— 
Tannin—While it was formerly assumed, simply on account of 
the black coloration with iron salts, that tannins are present in 
almost all plants, Dr. J. Dekker has shown by his investigations 
at Haarlem, that real tannins are comparatively rare and that there 
are whole natural orders which do not contain any tannin. The 
reaction with ferric chloride by itself is valueless as evidence ; only 
when it is confirmed by the reaction with a quinine solution and 
with a gelatin solution, is it possible to consider the presence of 
tannin established. It is therefore desirable to collect new and 
reliable data concerning the distribution of tannins in various 
natural orders, as was done experimentally by Dr. Dekker during 
the preparation of his monograph (which appeared as Bulletin 
Nos. 35 and 39 of the Colonial Museum at Haarlem) ; I have not 
neglected the unique opportunity at Kew of working on the same 
lines. A knowledge of tannins is very useful with regard to 
medicinal and technical plants and is also important in comparative 
phytochemistry. 
Alkaloids.-Our knowledge concerning the distribution of 
alkaloids in various natural orders is alread fairly complete, 
because we are here concerned with crystalline, well-defined 
substances of special medical or toxicological value, which are 
which, for nearly a century, have been diligently searched for by 
the pharmacists of the whole world. N evertheless, there are here 
also lacunae in our knowledge, and it was my object at Kew to 
attempt to fill these in some cases. Careful attention was therefore 
isolation and examination of the alkaloid. 
Hydrocyanic acid.—In the last two decades the occurrence of 
hydrocyanic or prussic acid (HCN) as a widespread constituent 
of plants has received so much attention, and has led in England, 
this report during his investigation paid attention to this sub- 
stance. Its presence frequently throws a remarkable light on the 
fatal toxic effects on man and animals often ascribed to certain 
plants and occasionally revealed by them quite unexpectedly. It 
becomes evident from this first report that a number of new 
so tried to delimit the known centres of the distribution of 
russic acid, Thi 
Ss is 
use the distillate of the plant is not required in the first instance 
