London Horticultural Society and Garden. 511 



of mucus at their extremities, concentrated by the power of adhesion, and 

 gradually acquiring the consistency of tissue. 



The Colour of stems differs from that of roots. Stems, till darkened by 

 exposure to the atmosphere, and other causes, are generally green ; but 

 roots, except those of two or three plants, never assume that hue. 



The Mode of Extension is also different. Stems throw out their branches 

 from nodes placed at certain intervals, and their position may always be 

 ascertained by some fixed rule : roots are always irregular, their fibrils 

 crossing and recrossing each other in every possible direction, and the in- 

 tervals between them being referable to no kind of calculation. 



The Power of Propagation possessed by stems is altogether deficient in 

 roots properly so called. It is barely possible that a radicle might, under 

 peculiar circumstances, produce an adventitious bud, in the same manner 

 as a leaf has been already shown to possess the power of doing ; but, when 

 such cases happen, they must be considered as exceptions from the general 

 rule, and must be regarded as a species of monstrosity. 



The Functions of the root, the professor observed, he had already men- 

 tioned, and it would be foreign from his purpose to dilate on them at pre- 

 sent, as it was his intention to recur to the subject in a future lecture. 



After thus enumerating the points of difference between roots and stems, 

 the professor proceeded to speak of the nature of the different kinds of 

 substances called by the general name of roots. He first observed that 

 though roots, properly speaking, are incapable of propagation by division, 

 several substances commonly designated as roots have that property. 

 Most of these substances may be classed under the names of tubers and 

 bulbs. Tubers partake greatly of the nature of stems ; and may be con- 

 sidered as prolongations of the stem under ground, containing accumula- 

 tions of fecula, formed from some unknown causes, as in the potato and 

 the Indian arrow-root ; probably intended by nature for the nourishment 

 of the young plant before the fibrils of its root have become sufficiently 

 strong to imbibe food for themselves. In all cases, tubers are furnished 

 with buds or eyes, which each possess a separate vital principle, and are 

 each capable of throwing out roots and a stem; 'in short, of producing a 

 perfect plant. The tubers of the arrow-root are oblong, and are attached to 

 the base of the stem by a slender ligament, which, as they advance towards 

 maturity, decays. The powder called Indian arrow-root is made from the 

 fecula contained in these tubers. Elongations of the stem of other plants, 

 partially thickened, often bury themselves in the earth, forming buds, and 

 throwing out stems and roots, so as to form new plants, as in the case of 

 the couch grass. 



Bulbs are, properly speaking, buds ; each containing in itself the embryo 

 of a new plant, and having roots proceeding from its base. Bulbs consist 

 of a number of laminae or scales, each scale being either the rudiment or 

 the residuum of a leaf. As new leaf-buds are formed in the axils of leaves, 

 so new bulbs or cloves (as in a root of garlic) are formed in the axils of 

 scales; and though not always developed, they exist in an inert state, and 

 are always capable of being called into action. Destroying the stem, and 

 affording an excess of nourishment to the parent bulb, would assist in 

 calling this dormant power forth ; and it has been said that this method is 

 sometimes employed in Holland, for propagating new or rare species of 

 hyacinth. The propagation of a valuable species of Zamia, under pecu- 

 liarly adverse circumstances, affords a striking proof of the practical use of 

 a knowledge of the physiology of bulbs. The Zamia is a plant with a large 

 bulbous stem, distinctly marked with dry hard scales, the bases of decayed 

 leaves, and crowned at the apex with a circle of large fern-like leaves, with- 

 out any other stem than the bulb from which they spring. A valuable 

 plant of this genus was sent to the botanic garden at St. Petersburgh ; but, 

 from want of care, or other incidental causes, it was found, when it arrived, 



