52 
ORGANOGRAPHY. 
BOOK I. 
6. Of Prickles. 
Prickles (aculei) are rigid, opaque, conical processes, 
formed of masses of cellular tissue, and terminating in an 
acute point. They may be, not improperly, considered as 
very compound hardened hairs. They have no connection 
with the woody tissue, by which character they are obviously 
distinguished from spines, of which mention will be made un- 
der the head of branches. Prickles are found upon all parts 
of a plant, except the stipules and stamens. They are very 
rarely found upon the corolla, as in Solanum Hystrix ; their 
most usual place is upon the stem, as in Rosa, Rubus, &c. 
Sect. II. Of the Stem or Ascending Axis, 
When a plant first begins to grow from the seed, it is a 
little body called an embryo, with two opposite extremities, 
of which the one lengthens in the direction of the earth's 
centre, and the other, taking a direction exactly the contrary, 
extends upwards into the air. This disposition to develope in 
two diametrically opposite directions is found in all seeds, 
properly so called, there being no known exception to it ; and 
the tendency is moreover so powerful, that, as we shall here- 
after see (Book II.), no external influence is sufficient to over- 
come it. The result of this developement is the axis, or 
centre, round which the leaves and other appendages are ar- 
ranged. That part of the axis which forces its way down- 
wards, constantly avoiding light, and withdrawing from the 
influence of the air, is the descending axis, or the root ; and 
that which seeks the light, always striving to expose itself to 
the air, and expanding itself to the utmost extent of its nature 
to the solar rays, is the ascending axis, or the stem. As the 
double elongation just mentioned exists in all plants, it follows 
that all plants must necessarily have, at an early period of 
their existence at least, both stem and root ; and that, con- 
sequently, when plants are said to be rootless, or stemless, 
such expressions are not to be considered physiologically 
correct. 
