THE PALM-STEM. 15 



parts. The youngest portion of the stem is frequently 

 clothed with a hair-like covering, so long as it is still 

 young and inclosed by the leaf-sheaths. Sometimes this 

 appears in the form of actual hairs, which are mostly 

 closely crowded and coherent into a dense felt ; e. g. in 

 Bactris tomentosa. In other cases, the covering is com- 

 posed of scales (ramentd), which exactly resemble those 

 of the Ferns ; e. g. in Rhapis flabeUiformis, Phoenix 

 dactylifera. In other instances the cells are combined 

 into spines of various dimensions. On the leaf-sheaths 

 and spathes many transitional forms are met with, from 

 simple hairs, stiff bristles, to strong, hard spines. Spines 

 of this kind exist on the stems of many Palms, lying 

 closely appressed to it, so long as the in tern odes are in- 

 cluded in the leaf-sheaths ; but erecting themselves after 

 the fall of the leaf, they form a terrible defence to the stem 

 by their hardness, length, and prickly points. 



The spines are sometimes blunt cones, but about an 

 inch long, as in Mauritia armata ; in Acrocomia sclero- 

 carpa, Astrocaryum Murumuru, Ayri, gynacanthum, &c., 

 on the contrary, they form long, slender, very hard and 

 acute needles. These are only cellular structures; the 

 cells of the outer layers are elongated, hard, and have 

 very thick walls, those in the middle are thin-walled 

 and parenchymatous ; the middle of the spine is often 

 hollow. 



Structure of the Vascular Bundle. 



Before I describe the modifications which the structure 

 of the vascular bundle undergoes in the different parts of 

 its course, it may not be out of place to state its com- 

 position in those situations at which, from the hard peri- 

 pherical cylinder of wood, it enters, on its way to the 

 centre, the soft middle substance of the stem. It here 

 consists of three constituents, which may be clearly dis- 

 tinguished from each other: 1, of liber; 2, of a bundle 

 of proper vessels (vasa proprid) ; and 3, of the ligneous 



