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 kno\^Ti 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 follow^s 

 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. 



