16 THE PALM-STEM. 



body. These three constituents are constantly applied 

 together in such a way that the liber is directed toward 

 the periphery, the wood toward the centre of the stem, 

 and the proper vessels lie between the liber and wood. 

 As a general rule, the following is the minute structure 

 of the different portions. 



The liber (Bast) consists of thick- walled, prosenchy- 

 matous cells. The opinion of Kieser, therefore (Phyto- 

 tomie, 209), that the liber-cells of the Monocotyledons 

 have horizontal septa, was altogether unfounded; and 

 indeed Moldenhawer (Beitrage, 48) had already found a 

 prosenchymatous liber in the Grasses. The liber-cells 

 manifest no definite arrangement in their corresponding 

 positions ; those lying toward the interior of the vascular 

 bundle are of the smallest diameter. They have fine 

 dot-canals (Tiipfelcanalen, canals of the pores). 



The proper vessels are composed of a combination of 

 much elongated cells, with horizontal septa, thin walls, 

 and of various diameter. The narrower lie partly between 

 the angles of the wider, partly between the lateral walls 

 of the others. 



The wood consists of elongated parenchymatous cells, 

 with thin walls, and porous, among which, on the side 

 directed toward the periphery of the stem, usually lie 

 two large reticulated vessels, and behind these a variable 

 number of narrower spiral and annular vessels. 



The structure described is not retained unaltered by 

 the vascular bundle throughout its whole length, but its 

 structure changes in the different parts of its course in an 

 analogous manner in all Palms. To demonstrate this, 

 two methods may be adopted, to investigate either the 

 transverse section of an entire stem, or an isolated vascular 

 bundle in the different parts of its course. 



In the investigation of the transverse section of a Palm- 

 stem, we can indeed become acquainted with the struc- 

 ture of any one of its vascular bundles only at one point 

 of its course; since, however, each of these vascular 

 bundles has a definite course from the periphery to the 



