SPOROPHYTE. 



19 



Only rarely do two elements lie adjacent radially. The walls are thick, 

 but not lig-nified, and are beset with deep pits with rounded, flaring- aper- 

 tures. They are best seen in the very young- regions (fig's. 107, 110) 

 where lignification is just beginning- to occur in the xylem (see table below). 

 The phloem forms a continuous ring-, one to three cells in thickness. 

 The cells are angular and appear in cross-section to be empty; their ends 

 (fig-. 65) acute, but not finely tapering-. These are sieve-tubes, but the 

 sieve-plates are only found with some difficulty . I could not demonstrate 

 callus, either with azoblue or coralline soda. 



TABLE ^.Measurements in millimeters of cells of various tissues in the stem. 



Between phloem and xylem lie the thin- walled, ang-ular, starch-laden cells 

 of conjunctive parenchyma (fig's. 63, 64, 81). They are about twelve 

 times as long- as wide, and have tran verse or oblique end- walls. Some of 

 these cells may extend in between the xylem tracheids, and rarely such an 

 extension joins with the inner conjunctive parenchyma, completely inter- 

 rupting- the xylem. Sometimes the conjunctive parenchyma is interrupted 

 and a sieve-tube lies directly against a scalariform tracheid. 



With the above exception the xylem is a continuous ring- of larger and 

 smaller scalariform tracheids, with thick, lignified walls (fig's. 63, 67, 97). 

 The middle lamella is clearly discernible. In places this ring- includes but 

 one radially widened xylem element; in other places it may be three cells 

 thick. There are no spiral elements in the stem. The tracheids are of 

 the usual long, pointed type (figs. 78, 79; see table above). 



The inner tissues so closely resemble the outer that they may be described 

 simply by comparison (figs. 63, 64). Conjunctive parenchymas show no 

 difference. The inner phloem is mostly one, often two, cells thick, and the 

 sieve-tubes are narrower than the outer ones (see table above). Proto- 



