12 THE PALM-STEM. 



interior. The thickening of their walls is usually indeed, 

 although always noticeable, not very striking, but in cer- 

 tain Palms, on the contrary, e. g. Diplothemum caudescens, 

 Cocos botryophora, they attain such thickness as we are 

 only accustomed to see in wood- and liber-cells. In conse- 

 quence of this thickening of the walls, the dots (which in 

 general occur in all Palm-stems) are converted into dis- 

 tinct canals, which correspond in contiguous cells. In 

 these two conditions, the thickening of the walls and the 

 punctation, these cells approach no less than in their 

 form, the cells of the medullary rays of Dicotyledonous 

 trees, since these also are constantly thick-walled and 

 punctated. 



The cellular tissue of the central part of the stem ex- 

 hibits in like manner many variations, which in great 

 part are connected with the position of the vascular 

 bundles. In all Palms it agrees in these characters the 

 cells are thin- walled, in most cases arranged in perpendi- 

 cular rows ; the cells lying upon the vascular bundles are 

 mostly somewhat elongated, and depend for the direction 

 of their transverse diameters on the position of the vas- 

 cular bundles. 



In the interior of the Cocos-\ike stems, the cellular 

 tissue exhibits a regular parenchyma, the cells are thin- 

 walled, finely punctated, and only in the investment of 

 the vascular bundles, or where two bundles lie near 

 together, do they form transitions to the muriform cellular 

 tissue, without, however, thereby acquiring thicker walls ; 

 in Cocos botryopJtora . and Diplothemium caudescens, the 

 cellular tissue even becomes thinner-walled the nearer it 

 lies to the centre. 



In most Palm-stems, on the other hand, in which the 

 vascular bundles stand much further apart in the middle 

 than at the circumference, the cellular tissue of the centre 

 exhibits considerable differences from that of the outer 

 layers, becoming very lax, and this in two ways. 



In some cases the cellular tissue in the middle of the 

 stem has very large cells, and thus forms a very soft, 



