-118 EXPLOITATION OF PLANTS 
desirable qualities of dyeing evenly and very exhaus- 
tively, and imparting weight to the material. The rare 
earths are now commercial commodities, and it is a 
question which can only be worked out in connection 
with technical experts whether the use of some of them 
as special mordants for certain adjective dyes may not 
enhance the value of the colours produced sufficiently 
to justify the extra expense of the mordant. 
In general, however, it seems poor economy, while 
we are still wholly dependent upon living plants for the 
fundamental necessities of food and clothing, to employ 
ground for cultivating dyes which we could substitute. 
quite well from the vast deposits of fossil plants. 
Where dye plants occupy terrain otherwise unpro- 
ductive, as in the case of the lichens, mangrove swamps, 
trees cleared from tropical forests, and the heather 
of oyr own moors, it is to our obvious advantage to 
exploit them where practicable. In other cases, e. g. 
in the indigo industry, much costly machinery would 
be out of action by the suppression of a long-estab- 
lished pliant industry. The policy, which seems to be 
indicated, is intense specialisation and efficiency in a 
few superfine dye crops, and the exploitation of new 
dye plants only from terrain which is otherwise of no 
economic value. 
REFERENCES 
KNECHT, Rawson and LoEwENTHAL. A Manual of Dyeing. Griffin & 
Co., London. 
Rawson, GARDINER and Laycock. A Dictionary of Dyes, Mordants 
and other Compounds. Griffin & Co., London. 
SEYMOUR ROTHWELL. The Printing of Textile Fabrics. Griffin & 
Co., London. 
E. M. Matret. Vegetable Dyes. Hampshire Press, London, 1916. 
