542 Bower—On the Primary Xylem , and the 
the first leaf: a similar origin applies also for the corresponding tissue 
opposite the later leaves of the plant previously described (compare 
PL XLV, Fig. 9). 
At the departure of the next leaf-trace of the plant cut by Dr. Lang, 
which is the fourth leaf in succession from the base, scattered tracheides 
appear in the pith, as seen in Fig. io. This leaf-trace, as well as those 
of all the subsequent leaves, departs, as was found by previous authors 
to be the case in mature plants, leaving an interruption in the external 
endodermis. But in this case it is plainly the result of that imperfect 
formation of the endodermal characters which is general in the older 
regions of these plants. The fading out of them may be clearly traced 
by passing upwards through the series of sections; for at the first separa¬ 
tion of the strand from the stele the endodermis is complete: as the trace 
passes out the endodermis yields, and remains complete for a time, but the 
staining reaction of the radial walls fails, and the failure is first seen 
externally to the trace itself, as shown in Fig. io for the fourth leaf. No 
internal endodermis extending into the pith was observed in any part of 
this plant. 
The structure thus seen in the two plants above described appears 
to be quite incompatible with any theory of intrusion of the cortex to form 
the pith, for the pith is present in both cases for at least four internodes 
below the first interruption of the internal endodermis, and structurally 
its origin is fully accounted for in relation to the intrastelar tissues. 
Moreover, the appearance of the scattered tracheides in the pith, at the 
level of the fourth leaf-trace in the second plant, appears to indicate a local 
reversion of the pith towards its original condition of xylem. This points 
to its phyletic origin having been, in part at least, by degradation of 
tracheides to parenchymatous cells. 
An examination of other young plants of B. Ltmaria shows that in 
respect of their medullation and in the behaviour of the endodermis in 
relation to the exit of the leaf-traces, they conform in essentials to what 
has been described; but there may be considerable variety in the exact 
details. The further elucidation of these will be necessary for a full under¬ 
standing of the stelar condition of the genus, and of the family at large. 
These observations on weak sporelings of B. Lunaria require com¬ 
parison with Van Tieghem’s results. They correspond in the main features. 
The chief difference lies in the question of the interruption of the endo¬ 
dermis. According to my own observations on young plants of B. Limaria 
the endodermis is not interrupted at the exit of the traces of the lower 
leaves. It remains continuous, and all the changes seen are strictly 
intrastelar. In the stronger and older state the endodermis fades out. 
It is believed that greater reliance may properly be placed upon the earlier 
data, and especially those seen in weak plants, than on those derived from 
