26 THE PALM-STEM. 



where these septa cut the axis of the vessel obliquely, and 

 therefore are elliptical in form, the fibres are mostly hori- 

 zontal. At the two rounded extremities of the septum 

 the orifices present the form of little slits or round holes, 

 in the middle of broad slits or oval openings, and at both 

 sides of the septum likewise occur smaller, roundish, or 

 ovate orifices. Each of these orifices is bounded by a 

 narrow rim. In other cases, the orifices exhibit the form 

 of narrow, transverse slits, giving the septum quite a 

 scalariform aspect. The openings are usually actual per- 

 forations, very rarely a thin membrane is stretched over 

 them. The fibres of the septa are double, and the rim 

 originates from the same cause as in the scalariform 

 ducts. These septa occur very frequently in the Palms ; in 

 many species, however, as for instance in Cocos nucifera, 

 they do not occur at every point of junction of two vessels, 

 for some of these end in the ring above described. To 

 avoid the necessity of recurring to these septa in the 

 examination of the root of the Palms, I will mention here, 

 at once, that in the large vessels of the roots the septa 

 are usually perpendicular to the axis of the vessel, and 

 therefore of roundish shape. In this case they are not 

 scalariform, but reticulated, perforated by large, roundish, 

 and many small punctiform orifices. The course of the 

 fibres does not always correspond exactly in the two com- 

 ponent plates of the septum, whence a portion of one 

 plate often projects into the opening of the other. 



In the porous vessels of the Dicotyledons it is well 

 known that vesicular cells often occur, which Kieser be- 

 lieved to be composed of the same membrane which forms 

 the wall of the porous vessel, whence he assumed (Phy- 

 totomie, p. 237,) that such vesicles could by no means 

 occur in the Monocotyledons. I however found, though 

 indeed but seldom, vesicular cells, similar to those of the 

 Dicotyledons, in the large vessels of the Palms, for in- 

 stance, in Corypha cerifera* 



* I have not traced the development of these cells in the Palms. Doubt- 

 less they have the same character as in the Dicotyledons, in regard to which 

 from recent researches, I think that I am not wrong in assuming that they 



