AN OLD-WORLD BOTANIST 
227 
is tantalisingly brief, and no data are given as to the amount of 
acidity present in the roots. How vitally important such con- 
siderations are, both to the purely scientific interest of the 
botanical physiologist, and also to the practical needs of the 
scientific agriculturist, may be seen by any one who cares to 
turn to the memoir, published a few years since, by Dr. Bernard 
Dyer.* 
Following up the clues afforded by the famous Rotham- 
sted experiments, which showed that, although there might be 
an enormous amount of ( e.g .) phosphates in a given soil, yet 
so little was assimilable, that a slight dressing of “ super- 
phosphates ” greatly increased the crop ; following up also a 
suggestion of Stutzer’s ; Dyer has shown, firstly, by a very large 
number of determinations, that the root-sap contains an acidity 
equivalent to about 1 per cent, of citric acid ; and, secondly, that 
a soil extracted with a 1 per cent, citric acid solution yields to 
the solution exactly so much phosphoric acid as corresponds 
with that found at Rothamsted to be taken up by the plants : 
in other words, the available phosphoric acid in a given 
soil — the amount that can be absorbed by a plant’s roots — is 
exactly that amount dissolved by a 1 per cent, citric acid 
solution. How great an importance this acidity of the root-sap 
now assumes it is needless to point out ; but let us return to 
Miller and see how far he had gone. He knew that the sap was 
acid, and more acid the nearer to the root ; he knew that, in e.g. 
the walnut, a “ tart ” juice was exuded if the root were cut ; and 
he supposed that there was a constant “ excretion ” from the 
root. It only needed one step further to anticipate the discoveries 
of over a century later, and to perceive in this acid root-sap a 
solvent of the soil-food ; but from this discovery Miller was 
barred — apparently by his obstinate notion that the acidity of 
the sap was a factor of its “ fossil” or mineral nature, and that 
an acid sap was imbibed from the earth. 
But to proceed : having disposed of the first class of juices 
he passes on to the second, viz., that of the leaves (which, as he 
rightly remarks, are the real lungs of the plant), of which juices 
he distinguishes three kinds, viz., (1) the nutritious, oily, and 
saccharine, juice of the leaves ; (2) wax ; (3) manna. 
The third class of juices is that of the flowers, which juices 
are subdivided into three classes also — (1) a volatile oil in 
which the odour resides; (2) an inodorous juice expressed from 
the flower ; (3) honey. 
The fourth class of juices are those of the fruit and seed, and 
the fifth class those of the bark.f After this account the reader 
will probably feel that, however much the “ learned Dr. Boer- 
haave ” may have edified the botanists of his own day, we of 
to-day are not greatly assisted by his classification of “ juices.” 
* See “Recent Work on Soil Analysis,” in Natural Science, May, 1896, for 
a summary, by the present writer of this work. 
t Which are subdivided into eight divisions, including gum, rosin, pitchy 
juice, &c. 
