24 THE PALM-STEM. 



with them. Since, as a rule, the vessels are surrounded 

 by elongated cells, and the lateral walls of these cells, 

 perpendicular to the vessel, run down some distance ver- 

 tically upon it, this causes the well-known appearance 

 that the dots or slits lie in a straight row, one above 

 another, in the vessel. In the Palms, the vessels are, in 

 most cases, surrounded by short, dodecahedral paren- 

 chyma; since, therefore, in accordance with the above 

 law, the pores are only formed at those places in the 

 vessel at which the parallel walls of the neighbouring 

 cells are grown to the wall of the vessels, these vessels 

 exhibit an apparently irregularly grouped distribution of 

 the pores and, between these groups of pores, free inter- 

 spaces, which correspond to the perpendicularly-placed 

 side and cross walls of the adjacent cells. 



In other cases, where elongated cells are in contact with 

 the vessel, the pores lie in regular vertical rows. When 

 two vessels are directly applied together, the pores of the 

 lateral walls, grown to the other vessel, assume the form 

 of transverse slits, which are as long as the breadth of 

 this wall, whereby the vessel becomes scalariform, while 

 the other sides, in contact with cells, possess the form of 

 the reticulated tube. These relative conditions are not 

 peculiar to the Palms, but occur in the same manner in 

 other plants, for instance, most distinctly in the Tree- 

 ferns. 



Obs. It is further to be noticed, that cases also occur in which the pores 

 have not the whole breadth of the adjacent elementary organ. For instance, 

 it not unfrequently happens that the pores are a good deal shorter, and lie in 

 regular horizontal lines, intermingled with longer slits. I found a peculiar 

 deviation from the general rule, that the pores of two adjacent vessels 

 correspond exactly in position, form, and size, in Corypha cerifera, where 

 one vessel was studded with longer slits, while the other possessed rows of 

 roundish or elliptical pores corresponding to these slits. 



Both the investigation of full-grown vessels and their 

 development, presently to be discussed, prove that the 

 pores and slits are not actual openings, but are closed 

 by a delicate membrane at the outside. This may be 



