306 
PHYSIOLOGY. 
BOOK II. 
chidaceae the root elongates independently of its extremity : 
— On the 5th of August I tied threads tightly round the 
root of a Vanilla, so that it was divided into three spaces, of 
which one was 7 inches long ; another 4 inches ; and the 
third, which was the free-growing extremity, If inch. On 
the 19th of September the first space measured inches; 
the second, 4f inches ; and the third, or growing extremity, 
2^ inches. A root of Aerides cornutum was, on the 5th of 
August, divided by ligatures into spaces, of which the first 
measured I foot 3 inches; the second, 2| inches; the third, 
3f inches; and the fourth, or growing end. If inch. On the 
19th of September, the first space measured 1 foot 3f inches; 
the second, 2| inches; the third, 3f inches; and the fourth, 
4| inches. 
Occasionally roots appear destined to act as reservoirs of 
nutriment on which those of the succeeding year may feed 
when first developed, as is the case in the Orchis, the Dahlia, 
and others. But it must be remarked, that the popular no- 
tion extends this circumstance far beyond its real limits, by 
including among roots bulbs, tubers, and other forms of stem 
in a succulent state. 
By some botanists, and among them by De Candolle, it 
has been thought that roots are developed from special organs, 
which are to them what leaf-buds are to branches ; and this 
function has been assigned to those little glandular swellings 
so common on the Willow, called lenticular glands by Guettard, 
and lenticelles by De Candolle. 
According to Knight, the energies of a variety artificially 
produced exists longer in the system of the root than in that 
of the stem ; so that it is more advisable to propagate old 
varieties of fruit trees from cuttings of the root than from 
those of the stem. 
The roots not only absorb fluid from the soil, but they 
return a portion of their peculiar secretions back again into 
it; as has been found by Brugmans, who ascertained that 
the Pansy exuded an acid fluid from its spongioles ; and by 
others, who found that various Euphorbiaceous and Cicho- 
raceous plants form little knobs at the extremity of their 
roots. Recently more important enquiries into this subject 
