THE STEM OF RHYNCHOPETALUM MONTANUM. 415 
cortieal system thus formed is permanent and capable of secon- 
dary increase. 
In Cycas the occurrence of this system of accessory bundles 
in the cortex may be regarded as a response to a physiological 
need. The vaseular bundles being the chief and most rapid 
channel of transfer of water and of nutritive materials, if Cycas 
were dependent only upon the girdle-like bundles of the leaf- 
trace for this transfer between stem and leaf, the channel would 
be very long and indirect. The accessory cortical bundles act 
in this case as short cuts, so to speak, reducing the distance 
Which must be traversed, and at the same time making the vas- 
cular connexions of the massive cortex much more complete. 
It can hardly be doubted that the bundles of the cortical system 
of Rhynchopetalum have a similar physiological function, though 
it must be confessed that the requirements are not so great as 
in the case of Cycas. 
In conclusion, it may be again noted that, not only in internal 
structure but also in external appearance the old stem of Rhyn- 
chopetalum resembles that of some Cycads. This is especially 
true for the lower portions of the old stem, where the increase 
of girth has been accompanied by the formation of fissures in 
the outer tissues, so as to obliterate the scars of the leaves. 
Such a case of similarity of stems of plants belonging to distinct 
classes should serve as a warning to paleontologists. It can easily 
be imagined that even a well-preserved fossil specimen of the 
stem of Rhynchopetalum might pass as that of a Cycad, and vice 
versa. 
DESCRIPTION OF THE PLATES. 
Lettering used throughout:—a=main cortical bundles; 4=secondary 
branches; r=normal ring of bundles in the stem ; z— median bundle of leaf- 
trace; y= first pair of lateral bundles of leaf-trace; z=second pair of lateral 
bundles of leaf-trace. 
Prats XXXVI. 
Upper portion of an old stem of Rkynchopetalum montanum seen from outside ; 
the spiral lines running over the leaf-scars indicate the position of the spiral 
cortical bundles. 
Prate XXXVII. 
Lower portion of the same stem as in foregoing Plate, showing the gradual 
obliteration of the leaf-scars by formation of longitudinal fissures. 
Prats XXXVIII. 
Fig. 1. Thick transverse section of a young shoot, made transparent with potash 
