the Sporophylts of the Cycadaceae . 239 
have taken place in certain forms, producing types like the 
Marattiaceae at an early period, so that the sporangia came 
to be borne on assimilating fronds, as in the case of most 
modern Leptosporangiate Ferns. On the other hand, the 
original type, viz., that in which the sporangiferous organs 
were distinct from the assimilating leaves, probably persisted 
right through, even down to the present day. From such 
forms as these latter I imagine it to be quite conceivable, and 
even probable, that modern Cycads took their origin. 
b. From the investigations of Solms-Laubach, Scott, and 
myself, it appears that the peduncle of these plants has in 
several ways, notably in the simplified vascular bundle-system, 
the presence of a mesarch structure in the bundles of the 
central cylinder, and of concentric strands in various parts 
of the organ, a more primitive structure than the vegetative 
stem, and probably therefore more nearly represents the 
original typical stem-structure. This being the case, it might 
naturally be expected that the foliar appendages of the 
peduncle would possess a more primitive structure than the 
foliar appendages of the vegetative stem. 
c. This primitive structure is represented by the concentric 
bundles which occur in both the fertile and barren sporophylls 
of several genera, especially in the latter organs, where the 
special physiological function of the former has not interfered 
with the original structure. These concentric bundles are 
absent from the foliage-leaves, the structure, number, and 
orientation of whose bundles are extremely regular, constant, 
and well-defined, whereas in the sporophylls the reverse is 
the case, a fact which probably points to their possessing 
a more primitive structure, viz., one not so perfectly adapted 
and stereotyped to subserve a special physiological function, 
as is the case with the foliage-leaves. 
In conclusion, the special point upon which I desire to lay 
stress in this paper is this : that though the sporophyll, 
according to my view, is a more primitive organ than the 
foliage-leaf, for the reasons above adduced, the main and, 
physiologically, most important part of its vascular structure 
