differences in the Structure of Stems, 243 



originated parts, which are formed exteriorly to the point of 

 departure. This is already evident without any examination, 

 and is so far from being a peculiarity of growth of the Mono- 

 cotyledons, that from this alone one might already have ven- 

 tured with security to conclude the non-existence of the pre- 

 tended Endogeneity. But it is most strikingly to be observed 

 in the separated closed vascular bundles of the Monocotyle- 

 dons ; although exceedingly well also in other cases, as for in- 

 stance in old Melocacti, Echinocacti, and Mammillarice. 



C. But here the most important circumstance is whether 

 the interfoliar parts are longitudinally developed or not. In 

 the first case all the new parts originating on the surface 

 (whether it be new vascular bundles or the continued develop- 

 ment of old ones) serve naturally to add to the thickness of the 

 whole stem, without its length being in any way increased by 

 these new parts. It is otherwise when the interfoliar parts 

 remain undeveloped. Here, as far as I have hitherto been 

 able to observe, this circumstance constantly occurs, that from 

 the germinating plant, or the node in the act of formation, the 

 impulse of growth, being unable to extend lengthwise, expands 

 every following internode more and more in breadth until a 

 certain period, so that every subsequent one projects somewhat 

 beyond the earlier one, and thus converts the original lateral 

 surface into an under surface. As the best example, I may here 

 mention the development of bulbs, and of the Melocacti. This 

 augmentation of the internodes continues only to a certain pe- 

 riod, namely, till the plant has in this manner formed for it- 

 self a sufficiently broad basis. From this time the new inter- 

 node no longer expands itself beyond the old ; and a stem gra- 

 dually increasing in height, but usually not increasing any 

 further in thickness, originates through the continued deposi- 

 tion of the interfoliar parts, resembling hollow cones, on one 

 another. A repetition of the gradual expansion of the inter- 

 nodes just described occurs as an exception in the tumid forms 

 of the palm stems. For the study of this form of stem in the 

 Monocotyledons, I would recommend to those who have not 

 palms at hand the Allium strictum and senescens, &c, as they 

 are in reality palm stems in miniature. 



From this mode of formation there naturally follows in those 



