LEAF IN THE VASCULAR CRYPTOGAMS AND GYMNOSPERMS. 
601 
localised at any point in the section, but as a comparison of a-d will show, is almost 
uniform throughout. 
For comparison with the leaf of Welwitschia some observations were made on the 
development of the phylloclade of Ruscus androgynus, with the result that in the 
main points there was found to be a close correspondence between them. In Ruscus 
the apical part of the phylloclade soon lost its meristematic activity, and the further 
growth was localised in the basal part of the organ, both in a longitudinal and trans¬ 
verse direction. Even the vascular bundles showed some similarity of arrangement, 
two lateral bundles being in advance of the rest. The only essential difference 
between the two structures is their point of origin relatively to the other members of 
the plant. 
Ephedra distachya . 
In order to complete the series, observations were also made on the leaves of Ephedra 
distachya, which are borne in whorls of three ; the upper part of each leaf is linear, but 
the basal part is winged, and the leaves of each whorl are united by the wings into a 
sheathing base. The development of the leaves is simple. Longitudinal sections of 
the apical bud show that the leaves arise as separate, lateral, conical protuberances on 
the conical apex ; the growth and cell-division are at first uniform. When the young 
leaves have advanced so far as to overtop the apex of the stem, active meristematic 
division at the apex of the leaf ceases, but it is continued at the base. This becomes 
still more apparent in older leaves. Thus the greater part of the leaf owes its origin 
to intercalary growth at or near the base of the leaf. This is accompanied by a 
winged development at the base, the growth extending to that part of the axis which 
intervenes between the members of one whorl: thus the sheath-like structure above 
noted is the result. Tranverse sections (Plate 40, fig. 55, i.-iv.) show that the leaf is 
here also essentially a winged structure, though the wings are reduced : still the 
similarity between this leaf and that of Gnetum and many Coniferce is not difficult to 
trace. 
For the development of the elongated cotyledons no material was at hand, but I 
should conclude from the structure of almost mature ones, as well as from their mode 
of growth during germination, while the seed is still retained at their apex, that they 
increase by intercalary growth. 
Conclusion. 
It remains to draw together the results which have been obtained from the investi¬ 
gations above detailed. We are now in a position to state the characters of the phyl- 
lopodium in the lower forms of vascular plants, and then to follow those characters 
through the intermediate forms, and trace their modification as we progress towards 
MDCCCLXXXIV. 4 II 
