Anatomy of the Ophioglossaceae. I. 205 
is attained, but the leaf-scars and roots are closely crowded, and there 
is no appearance of specially elongated internodes. Often, however, an 
intermediate region is present between the basal and the adult regions ; 
in this intermediate region the rhizome is slender and the leaf-scars and 
roots are distant. It is of variable length, being sometimes represented by 
one or a few internodes, while in other cases it attains a length of several 
inches and bears a considerable number of leaves. Possibly the occurrence 
of this slender elongated region, and its greater or less development, may be 
related to the depth of the parent prothallus beneath the surface of the 
ground. Above the intermediate region, when present, the rhizome increases 
in diameter rather suddenly and then maintains the greater diameter. 
In this adult region the leaves and roots are again crowded, and there is no 
appearance of internodes. 
The distinction here made on the ground of external form between 
basal, intermediate, and adult regions of the rhizome has to be borne 
in mind in considering the anatomy. When the stelar structure is followed 
from below upwards the basal region is found to exhibit the transition from 
a solid protostele to a medullated stele. In the region above this a 
medullated stele with a distinct ring of primary xylem, but little or no 
secondary thickening, is met with. When the intermediate region is marked 
the leaf-gaps are frequently very long, and it is in this region that the 
internal endodermis discovered by Poirault, and recently re-described by 
Bower, may occur. A transitional region with increasing development 
of secondary wood around the primary xylem leads to the adult region ; in 
this the much larger stele has a marked development of secondary xylem, 
the leaf-gaps are short and often overlap, and an internal endodermis is 
always wanting. 
The nature of the secondary thickening in Botrychium Lunar ia will be 
discussed with some other points of detailed anatomy below. It will be 
convenient first to consider the general progression in stelar structure from 
the basal to the adult regions of complete plants, the relations of the 
external endodermis to the internal endodermis when the latter is present, 
and the bearing of these facts on the nature of the pith. 
Progression in Stelar Anatomy from the Basal to the 
Adult Regions of the Rhizome. 
For the study of the vascular skeleton of B. Lunaria six small plants 
were cut into complete series of transverse sections. The results obtained 
by detailed examination of these plants are recorded in the accompanying 
reconstructions of the vascular system (Text-figs. 3-8). The results have 
been checked by less complete study of larger plants and by comparison 
with longitudinal sections. In this way it has been possible to analyse the 
facts in greater detail than was done by Bower in the paper in which he 
Q 
