GROWTH OF THE STEM. 



31 



iutemally of a cellular tissue, representing the 

 medulla, and externally of tubes or fibres, con- 

 stituting the fii-st rudiments of the wood, the 

 bark, and in general all the filamentous parts of 

 the stem. We proceed to examine a palm-seed 

 at the period of gennination. Its radicular 

 extremity elongates more or less, bursts at its 

 summit, to permit the escape of the radicle, 

 which was previously imprisoned in a kind of 

 closed bag, named the coleorhiza, which it teare 

 in order to penetrate into the ground, and be- 

 come the root. The opposite extremity to the 

 radicle, the cotyledon, assumes a slight develop- 

 ment, but is presently seen to split on one of its 

 sides, beneath its summit ; and through this slit 

 or rupture, issues a variable number of leaves, 

 at first, embracing each other. But in this 

 embryo of the palm, we see no rudiment of the 

 stem, as in the embryo of the oak, lime, pine, 

 and other dicotyledones. The organ to which 

 that name is ultimately given, has to be gradually 

 formed at the expense of anotlier organ. As we 

 have already explained, the bases of the leaves 

 which are successively developed, approaching 

 closer to each other, in consequence of the pres- 

 sure exerted upon the outermost, in proportion 

 as new ones are developed w-ithin, adhere to- 

 gether, and ultimately form a kind of fleshy 

 platform, composed of cellular tissue, and tra- 

 versed by scattered fibres. What is called the 

 stipe or trunk in the palm, is therefore an organ 

 composed of a great number of scales, which are 

 only the bases of leaves more or less united 

 together, and presenting at their interior a cen- 

 tral and terminal bud, which is its essentially 

 vegetating organ. Thus, then, the stipe of a 

 palm is not really a stem, whether we consider 

 it as to its origin and development, or its organi- 

 zation. Something of this same nature occurs 

 in other plants, especially in the subterranean 

 stem, or what is commonly called the root, of 

 the genus iris. It is a fleshy body, having some 

 longitudinal fibres in its interior, and present- 

 ing, at its outer surface, the cicatrices of the 

 scales which compose it. If we follow its de- 

 velopment, we find that it owes its formation 

 to the bases of the leaves, which having remained 

 unwitliered, while their upper part has been de- 

 stroyed, have united together and formed the 

 fleshy body, which, in the genus iris, is com- 

 monly designated by the names of root, rhizoma, 

 stock-root, or subterranean stem. Conse- 

 ([uently, this organ, like the stipe of the palms, 

 is in reality neither a root nor a stem, but a 

 collection of bases of leaves all united into a 

 single mass. A species of garlic, allium sene- 

 scens, presents an organ precisely similar, being 

 a more or less fleshy and branched stock. From 

 this stock of allium senescens and the genus iris, 

 does there not appear to he a gradual transition 

 to the solid or scaly bulb^ of the lilies ? A 



bulb is merely an organ composed of scales, 

 varying in their form and disposition, but al- 

 ways seated on a fleshy platfonn, and covering 

 a central and terminal bud ; while the scales 

 themselves are nothing but leaves, whose base 

 alone is developed, or whose base alone has re- 

 mained unwithered, while the upper part has 

 been destroyed. If, as has been presumed, the 

 subterranean stock of the u-is has the same 

 origin, the same mode of development, and the 

 same organization as the stipe of the palms ; and 

 if, on the other hand, there is no perceptible 

 difi^erence between the alleged stock of the 

 iris and the bulb of most of the lilies, it ap- 

 pears impossible not to draw the conclusion, 

 that the stipe of the palms, in place of being a 

 stem, is in fact merely a bulb. This opinion 

 might seem paradoxical to a person who should 

 not overlook the general form, the size and 

 duration of the stipe of the palms, compared 

 with the bulb of other monocotyledonous plants. 

 But if we reflect attentively that these different 

 properties are ncrt essential to the nature of that 

 organ; that they are often wanting in a great 

 number of species; that in some the stipe, in 

 place of being long and cylindrical, is short, 

 scarcely perceptible, and sometimes consists 

 merely of a kind of bulbifonn enlargement ; 

 that, in other species, this stipe, so far from 

 being hard and woody, is soft and fleshy, and is 

 easily penetrated by cutting instruments, these 

 differences, which at first seem so striking, in- 

 stantly disappear. If, on the other hand, wo 

 examine the origin, the mode of formation, and 

 the manner of growth of the stipe compared with 

 those of the bulb, we must conclude that the 

 two organs are essentially the same. 



In this manner of viewing the stipe, we can 

 easily account for the circumstance of its being so 

 rarely branched. It is well known that a branch 

 is never any thing else than the result of the 

 elongation of a bud, generally placed in the 

 axilla of a leaf. Now, in the monocotyledones, 

 these axiUar buds are almost always abortive, 

 or remain in the rudimentary state, as in most 

 of the grasses. This is also the case in the 

 palms : their axiUar buds generally remain in the 

 rudimentary state, and then the stipe is perfectly 

 simple ; but, in certain circumstances, some of 

 these buds receiving more nourishment than the 

 rest, are developed, or in other words, the leaves 

 composing them, which unite together at their 

 biise, ultimately form a new stipe proceeding 

 from the first. This is what takes place in cer- 

 tain species oi yucca, in the Doom Palm of Upper 

 Kgypt, &c. 



Hitherto the growth in diameter was generally 

 admitted as the exclusive result of the new 

 layers which are added every year between the 

 alburnum and baik. Dutrochet has proved 

 that vegetables increase in diameter in two diiec- 



