STRUCTURE.] DOOM PALMS ANOMALIES. 225 



be received with caution. It may further be remarked, with 

 reference to this subject, that in many Palms these rings 

 disappear after a certain number of years. 



In arborescent Endogens it usually happens that only one 

 terminal leaf-bud developes ; and in such cases the stem is 

 cylindrical, or very nearly so, as in Palms. If two terminal 

 leaf-buds constantly develope, the stem becomes dichotomous, 

 but the branches are all cylindrical, as in Pandanus and the 

 Doom Palms of Egypt ; but if axillary leaf-buds are regularly 

 developed, as in the Asparagus, Dracaena Draco, or in arbor- 

 escent grasses, then the conical form which prevails in Exogens 

 exists in Endogens also. 



In Endogens there are but few important anomalies in 

 structure ; and of these the most striking, namely that of 

 Grasses, is more peculiar than anomalous. Yucca appears, 

 from a figure of Meneghini (Ricerche sulla Struttura del Caule 

 nelle Piante Monocotyledons, t. ix. f. 1. c.), to arrange its woody 

 bundles in concentric layers when old ; Smilax has a stem 

 strictly endogenous, and a root which approaches in structure 

 the stem (not root) of Exogens ; and, in the article Endogens, 

 in the Penny Cyclopaedia, I have shown that the stem of 

 Barbacenia is composed of roots of an endogenous nature, 

 held together by the adhesion of their cortical integument, 

 and that of a very slender central true stem on which they are 

 moulded. In Grasses the stem is hollow except at the nodes, 

 where transverse partitions intercept the cavity, dividing 

 it into many cells. In the Bamboo these cells and parti- 

 tions are so large that, as is well known, lengths of that plant 

 are used as cases to contain papers. But if the gradual 

 development of a grass be attentively observed, it will be 

 found that the stem is originally solid ; that it becomes hol- 

 low in consequence of its increasing in diameter more rapidly 

 than new tissue can be formed ; so that its deviation from 

 the ordinary characters of Endogenous structure is much less 

 considerable than it seems to be at first sight. 



According to Mohl, the structure of an Exogenous and an 

 Endogenous stem, during the first year of their growth, is 

 altogether the same ; but in the second year the wood and 

 the liber of the former separate, and new matter is then 



VOL. T. Q 



