Phytogeny of the Cyperaceae . 2 1 
Here are certain Calycanthaceae and Melastomaceae, in the first of 
which the cortical bundles show a reversed orientation of xylem and 
phloem. Thirdly, the central and larger lateral leaf-bundles enter directly, 
while the marginal bundles become cortical, as in certain Aroideae, 
Palmae, Bromeliaceae, and most of the Scitamineae. Fourthly, it rarely 
happens that the middle leaf-trace bundle passes down through the 
cortex to a lower node, while the lateral strands join directly with the 
cauline system, as in A rceuthobium. 
Van Tieghem (56) has suggested a possible explanation of the 
cortical course of the leaf-trace upon the hypothesis that the leaf-sheath 
has fused with the stem for one or more internodes above its actual 
origin. Some weight is lent to this view by the mode of leaf-insertion 
observed by the writer in Streptopus. Here, especially in S', ample xifolins, 
the margins of the leaf- base are frequently fused with the stem for two 
centimetres or more above the nodal complex. 
In the scapose Cyperaceae the bundles of the involucral bracts 
enter the stem in a broad curve and unite with the medullary bundles 
at the basal part of the nodal complex, in a manner very like that 
prevailing among the Liliales. A similar mode of leaf-insertion is found 
in the nodes of Scirpus robustus . Accordingly, these forms show no 
cortical fibro-vascular bundles, though the deep-seated cortical sclerenchyma 
strands may be vestigial indications of a cortical system of bundles. 
The culm of the Cyperaceae does not normally branch except in 
giving rise to the axes of the inflorescence. However, abortive axillary 
buds are of very common occurrence. The fibro-vascular strands supplying 
these buds are always collateral, and may be traced downward to their 
insertion upon the cauline bundles just below the nodal plexus. They 
have no direct connexion with the leaf-trace, differing in this respect 
from the axillary buds of certain Liliales described by Queva (38), and 
also from those of A Ichemilla described by De Candolle (13), as well 
as from the Palm type of Mohl (33). It is important to note that in 
the Cyperaceae the ramular bundles have nothing to do with the nodal 
amphivasal plexus, contrary to the principles laid down by Queva (38), 
in connexion with his study of Gloriosa , This point will be referred 
to again in considering the floral axis. 
The Leaf. 
The narrow linear leaves of the Cyperaceae, without exception, present 
a strongly xerophytic type of structure. In all cases they surround the 
stem for a considerable distance by a closed sheathing base. The free 
lamina is usually deeply grooved, presenting a V-shaped cross-section 
in the narrower forms, while the broader ones show a horizontal portion 
extending outward from the end of each arm of the V, as in Carex lupulina. 
