THE PALM-STEM. 23 



of the tubes do not lie one behind another in the direc- 

 tion of a line drawn from the periphery to the centre of 

 the stem, but side by side. The tubes do not always 

 succeed one another singly in the longitudinal arrange- 

 ment, for frequently two or three stand next below a 

 single one, so that in the cross section there appear to be 

 2 3 vessels side by side. This occurs sometimes even 

 low down in the vascular bundle, in which case these 

 vessels often again blend into a single one. Some of 

 these vessels attain a very considerable size. In the 

 lower part of the course of the vascular bundle, they 

 have indeed scarcely a diameter of ^ of a line ; but the 

 vessels occurring in the middle tract are among the 

 largest that are met with in the vegetable kingdom : 

 thus the vessels of Bactris mitis exhibit a diameter of 

 from ^ to of a line, those of Desmoneus mitis, (Enocar- 

 pus minor, ~ to ^, of Astrocaryum gynacanthum ~ to ^, 

 Corypha cerifera and Mauritia armata to ~, Mauritia 

 vim/era \ to \, Calamus Draco i to J of a line. 



The walls of these vessels universally exhibit the form 

 of a dotted tube.* But the nature of this varies according 

 to the nature of the adjacent parts. As this circumstance 

 has almost entirely escaped phytotomists, a more minute 

 exposition of it may not be out of place here. I have 

 already pointed out, that in cellular tissue the position of 

 the pores of one cell exerts a definite influence over the 

 position of the pores of the adjacent cells, and that the 

 pores of two contiguous cells always correspond. Now this 

 occurs also in the reticulated vessels. It is a universal 

 law in the reticulated vessels and scalariform ducts of all 

 plants, that the dots and slits of their walls are somewhat 

 shorter than the breadth of the cell or vessel in contact 



* In the Latin original I have called them vasa porosa, v. punctata, 

 because the term reticulated vessel did not appear to me adapted to the 

 kind of punctation. But since I have subsequently found that the pores of 

 dotted vessels of the Dicotyledons are distinguished from those of the vessels 

 of Palms, by the fact that there is a cavity between each pair of pores in the 

 former, which is wanting here, I now select the expression reticulated vessel, 

 to avoid the necessity of making a new term. 



