2i6 Lang . — Studies in the Morphology and 
and adult regions. In the intermediate region a more or less complete 
internal endodermis is present, extending over the origin of three leaf-traces. 
The distribution of the internal endodermis, which can be followed from 
the series of cross-sections and the reconstruction (Text-fig. 8), does not 
lend support to the idea of pocketing at the leaf-gaps. It is limited to the 
slender intermediate region, while in other respects the medullation of the 
stele does not differ from what is found in the regions below and above. 
Both the transverse sections and the reconstruction show how, after the 
stele has widened from the base of the plant (j-^), its diameter decreases 
greatly in the intermediate region (6-12) and then increases again till the 
uniform diameter of the adult region is attained (19-21). 
Comparison of the vascular systems of these six small plants of 
B. Lunaria allows of a number of conclusions being drawn with tolerable 
certainty. On the whole, the distribution of the leaves and roots suggests 
a repetition of corresponding segments of the plant body whatever the 
ultimate explanation of the segmentation may be. Usually one or two 
roots are inserted on the stele close to the sides of the leaf-gap just after 
a leaf-trace has separated. There is not, however, a rigid relation of roots 
to leaves, for a number of leaf-traces may be given off without any corre- 
sponding roots. It may further be noted that it is difficult to distinguish 
nodes and internodes in B. Lunaria. When a long internode appears to be 
present this is found to be due to the extension both of the region in which 
the trace is gradually separating from the stele and of the leaf-gap left on 
the separation of the trace. Both these regions may be regarded as belong- 
ing to the leaf-base. The result attained is, however, the same as if definite 
nodes and internodes were present ; the longitudinal extension of the shoot 
is increased, and the individual leaves are more widely separated. In this 
way the distance between a departing leaf-trace and the nearest roots below 
may be greatly increased, as is seen most clearly in the fourth leaf-trace of 
plant E. 
All the plants showed a similar transition from a stele with a solid xylem 
to one with a pith. The appearance of a pith in the stele was never asso- 
ciated with the presence of an internal endodermis, and the transition from 
the basal region to the typical adult structure may be a direct and gradual 
one without the development of an internal endodermis in any region. The 
transition to the adult type of relation of leaf-trace to stele may take place 
close to the base of the plant (Plant B), or a number of the lower leaf-traces 
may depart without leaving endodermal gaps (Plant A). In both these 
cases, while there is a gradual increase in the size and complexity of the 
stem and its stele, there is no specialized intermediate region to be dis- 
tinguished. 
The development of an internal endodermis appears to be associated 
with the presence of a definite intermediate region, in which there has been 
