230 LIMITED BUNDLES. [BOOK i. 



form of annular, spiral, reticulated, or porous tubes, and 

 ligneous cells ; the latter, whether uniform or different, form- 

 ing the wood, properly so called. Up to a certain period the 

 development of the woody bundles proceeds in the same 

 manner in both Monocotyledons and Dicotyledons ; but after 

 a time, in Monocotyledons, the fast-growing, thin-walled 

 cellular tissue suddenly changes, the partitions of its cells 

 become thicker, their power of producing fresh cells ceases, 

 and, as soon as all the surrounding cells are fully grown, a 

 new and peculiar form is assumed, and gum, mucilage, &c., 

 or other dense organisable matter ceases to be conveyed. 

 At the time when the development of these cells ceases, they 

 are called by Mohl vasa propria. Owing to the circumstance 

 just explained all further development of these woody 

 bundles is rendered impossible, and, therefore, I call them 

 LIMITED (geschlossen.} In Dicotyledons, on the contrary, 

 this tissue, which is in such plants termed cambium, by 

 authors, or couche regeneratrice, by Mirbel, retains its vital 

 power during the whole life of the plant, continuing to 

 generate new cells, which thus increase the mass as they go 

 on, adding partly to the exterior, (liber,) and partly to the 

 interior, (wood,) for an indefinite time. This takes place 

 according to the climate and nature of a plant, either with 

 little interruption, as in the Indian Figs, (Cactacese,) or 

 periodically, rapid formation alternating with almost entire 

 cessation of growth, as in our forest trees. In the latter, a 

 little perseverance and delicate manipulation proves, that the 

 stem forms a continuous tissue, from the pith to the bark, at 

 all periods of its life, and that the bark never really separates 

 from the stem ; what has been called a separation being in 

 fact a mere rending asunder of the delicate tissue called 

 cambium, which is really present, even during winter, and 

 thus lays the foundation of a new annual zone, although 

 it is compressed, and filled with gum, starch, or other sub- 

 stances. In the spring, it is expanded and swollen by the 

 current of new sap, and its contents are dissolved out. In 

 all cases it may be shown conclusively that the new cellular 

 tissue is always formed within that already existing, that is 

 to say, iii primitive cells, by means of cytoblasts, in the 



