Hymenophyllaceae , Schizaeaceae and Gleicheniaceae . 523 
dermis separating this tissue from the xylem, and this fact 
also determined Russow (7 2, p. 97) and De Bary (77, p. 344) 
to regard the central tissue as belonging to the bundle-tissue. 
Structure of the Mature Plant in other Species. 
Schizaea bifida need not be specially described. In struc- 
ture it resembles 5. dichotoma, but its parts have smaller 
dimensions. Endodermal pockets are present, but neither 
inner endodermis nor internal tracheides were found. Further 
material of 5. digitata has also been examined, but none of 
the complications of structure shown by S', dichotoma were 
present in the specimens sectioned. 
Young Plant of Schizaea pusilla. 
The life-history of this species has been described by 
Britton and Taylor (’01). A figure of the mature stem (in 
transverse section) of this species is given by these authors 
(’01, PI. V, Fig. 80), but the transitional region is not dealt 
with. Seedling-plants of S. pusilla were sectioned with the 
microtome. The largest of these plants, examined in an 
acropetal series of sections, shows the stele becoming imma- 
ture between the fourth and fifth leaf, but previously the 
mature type of structure usual in the genus had been prac- 
tically attained, so a description of the series is worth giving. 
The main root appears to be diarch ; the transition to 
protostelic stem-structure takes place in the usual way, the 
tracheides becoming more uniform in size and surrounded 
by phloem (Fig. 36, A). When the first leaf-trace separates 
from the stele, it leaves only three tracheides ; on the separa- 
tion of the second leaf-trace 6-8 tracheides remain in the 
stele ; these increase, after the attachment of the second 
lateral root, to about 15, the xylem of the stele being still 
solid. Parenchymatous cells next make their appearance 
in the xylem (at first only two of them), and they and some 
of the tracheides undergo change of position, so that the 
parenchyma-cells are sometimes completely shut in, some- 
times not. When the xylem of the third leaf-trace separates 
