140 PLANT ANATOMY, 
roots. ‘The younger roots of Belladonna lose as much as eighty- 
five per cent of water; Radix Tarazaci, seventy-seven per cent, 
and juicy fruits still more. All parts of plants, however, retain 
water which we are wont to designate as hygroscopic water, but 
which by no means exists in the cells in a liquid form. The 
amount of this varies very considerably according to the nature 
of the tissues, and presumably also according to their con- 
tents. 
The squwiil, which is rich in sugar and mucilage, retains four- 
teen per cent of hygroscopic water, Radix Gentiane sixteen to 
eighteen per cent, and saffron about twelve per cent. If these 
substances are completely deprived of water in a drying-closet, 
or in the cold over sulphuric acid, and are again exposed to the 
ordinary conditions of preservation, they quickly absorb again 
about the same amount of water. Drugs which do not have a cel- 
jular structure likewise contain definite amounts of water; per- 
fectly air-dry starch, gum arabic, and tragacanth, for example, 
thirteen to seventeen per cent. Seeds, on the contrary, and es- 
pecially those provided with a hard testa, are capable of retaining 
but a few per cent of water. 
After the evaporation of the water, dissolved substances are 
deposited in a solid form, as has already been mentioned when 
speaking of inulin. Only a limited number of substances in- 
soluble in water are capable of preserving in the dry tissue so 
liquid a form as to flow in drops. Such are the volatile oils, the 
boiling point of which lies from 70 to 150 degrees or more 
above that of water, in consequence of which they evaporate only 
to a slight extent with the water at ordinary or only slightly 
elevated temperatures, and are still further retarded in this re- 
~ spect when they contain resins in solution. 
It is remarkable that the milky juice of Jalap also still pos- 
sesses, in the dried drug, a liquid form, and indeed the resin pre- 
pared therefrom is capable of retaining water very obstinately. 
Besides the loss of water, and probably also of a portion of the 
volatile oil, many plants experience, upon drying, chemical 
changes, regarding which we are indebted to Schoonbroodt ' for 
* Wiggers-Husemann’s Jahresbericht, 1869, 9. 
