PHANEROGAHIA I AXIAL ORGANS. 257 



perspicuity, much less, as did happen, have served as a temporary basis 

 for theories pervading the whole science of Botany. 



The first is the idea of Desfontaines of the distinction between Mono- 

 cotyledons and Dicotyledons, that the former develope new structure in 

 the centre of the axis, and grow in the inside (plantce endogence), while 

 the latter produce ligneous substance close under the bark, and deposit 

 it on the inner side, and thus grow on the outside (pi. exogence). All 

 this had no greater foundation than the fact that in the Mondcotyle- 

 donous axis the vascular bundles are farther apart in the centre ; conse- 

 quently, in the preponderance of parenchyma, the substance is more lax. 

 It was not ever attempted to make even a superficial observation of the 

 process of growth; if it had been merely observed that the vascular bundles 

 going to the lower leaves, consequently the older, crossed those going 

 to the upper leaves, which must be the younger, a child might have 

 been made to understand at once that a growth of new vascular bundles 

 in the interior was an absolute impossibility. Nevertheless, upon this 

 empty fancy, which a child might have refuted, De Candolle built a grand 

 system of vegetables, which it never did require the distinguished and 

 comprehensive researches of Mohl to overthrow. 



The second notion is that of Du Petit Thouars, which was not less 

 ill-grounded, which, as expressed by him, would be upset by every, 

 even the most superficial observation, and even in its more refined subse- 

 quent statement is by no means established, but has important and ap- 

 parently irresistible objections against it. Du Petit Thouars thought 

 that all increase of thickness of the axis resulted from the descent of 

 roots from the buds. Such a crude notion scarcely required refutation. 

 On the other hand, it was afterwards stated that the formless but or- 

 ganisable substance (the cambium) was gradually organised from the 

 buds downwards. The only possible foundation for this view, namely, 

 evidence obtained by thorough investigation of the history of develop- 

 ment, is still due from all its assertors, the latest, Gaudichaud, &c., in- 

 cluded. Therefore it is already to be set aside as devoid of foundation. 

 But the contrary can be made good, that, in the first place, no cambium 

 ever exists as a formless fluid in the plant, unless we would so call the 

 cytoblastema enclosed in the cells ; secondly, that, so far as observation at 

 present reaches, cells are always formed in cells, that this cell-formation, 

 according to the observations I have made in the Cactacece, &c., pro- 

 gresses from below upward ; thirdly, that the axillary bud is already 

 formed in the terminal bud before the axis begins to increase in thickness, 

 and that certainly the cells of the bud are organised into vascular bundles 

 from the vascular bundles of the stem upward into the bud, and not in 

 the reverse direction. By these remarks the whole notion seems to me 

 to be for the present set aside, and it would require quite other support 

 than that which Gaudichaud's imperfect attempts in anatomy and phy- 

 siology could give it. 



Lastly, I must notice the most recent views of Martius on the struc- 

 ture of the stems of Palms, &c. Martius asserts, that here the vascular 

 bundles, the primary structure of which is sketched out in the conical 

 terminal bud, on the whole, as I have already explained it (Wiegmarn's 

 Arcliiv, 1839, 219.*), do not merely grow upwards into the leaves, but 

 also downward, by their lower end, in the stem. These facts I must 



* Beitraige zur Botanik, vol. i. p. 29. 

 3 



