Phylloglossum Drummondii. 
337 
observed in the longitudinal and transverse sections does not, however, 
justify the conclusion that this meristem focuses upon a single apical cell. 
In the meantime the sections have passed through the older tuber 
(Fig. 4)* This latter, it will be seen, is really the tuber of the current 
season, the younger one, described above, being the tuber for the following 
season. 
Fig. 3. Diagram of median longitudinal 
section, y.t.s., strand of young tuber ; s.s., stem- 
stele ; r.t., l.t ., root- and leaf-trace; other letters as 
in Fig. 1. The numbers 2, 4, 5, 6, 7 indicate the 
levels at which the transverse sections shown in 
Figs. 2, 4, 5, 6, 7, respectively, were taken. The 
shaded portion denotes the meristematic tissue of 
the growing tuber. Xylem in thick black lines. 
Fig. 4. Transverse section of young 
tuber, showing central cavity ca, with two 
merismatic cells at its edge. The older 
tuber ( c.t .) also appears in section. 
The older tuber presents a highly lacunar appearance below. This 
would be significant, but it is doubtful whether this is not due to indifferent 
preservation; there is no indication of lacunar structure in the parenchy¬ 
matous tissue further up in the tuber—the aeration of the stem and tuber 
being provided, apparently, chiefly by the loose packing of the parenchyma 
cells. 
Returning to the younger tuber, a few wood-elements appear, shortly 
above the extremity of the ‘ channel ’, in the centre of the sections (see 
Fig. 3). At no level do these exceed about a dozen in number; and in 
z 
