254 
PHYSIOLOGY. 
BOOK II. 
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 7 J 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 1 foot 
3 inches; the second, 2 J inches; the third, 3 J inches; and the 
fourth, or growing end, 1 J inch. On the 19th of September, 
the first space measured 1 foot 3 J inches; the second, 2 J 
inches ; the third, 3 J 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 exist 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 Cichorace- 
ous plants form little knobs at the extremity of their roots. 
Recently more important enquiries into this subject have 
been made by Macaire, who, in a paper in the Transactions 
