Phytogeny of the Cyperaceae . 3 
9. What is the position of the Cyperaceae among the Monocoty- 
ledons? 
10. What bearing have the observed facts upon the phytogeny of the 
Monocotyledons as a whole ? 
Before entering upon a discussion of these problems it will be neces- 
sary to consider in more or less detail some of the structural characteristics 
of representative genera and species of the Order. 
The Root. 
The internal structure of the root in the Cyperaceae presents a 
striking degree of uniformity. The central cylinder is compact and rela- 
tively small, surrounded by a well-marked endodermal sheath, the cells of 
which commonly have the inner wall much thickened. The medulla is 
composed of round, more or less sclerotic cells of relatively small size, with 
sharply-defined intercellular spaces. The xylem masses are radially 
disposed within the bundle-sheath, alternating with the phloem masses. 
Their number is variable, but rather smaller than that found in the majority 
of Monocotyledons, ranging from six to eight in species of Eleocharis to 
fifteen to eighteen in certain Carices, while, according to Kny (32), these 
numbers may approach or even exceed too in the roots of some Palmales. 
Each xylem-mass consists of a few short, small, thin-walled tracheids 
arranged in a radial plate terminated centrally in a single relatively large 
vessel. It frequently happens that there are not as many large vessels as 
there are xylem-masses, in which case growth pressure may cause a vessel 
to lie at the point of a V of which the arms are two distinct xylem-masses, 
which are brought in this way to subtend the intervening phloem-mass, in 
a manner remotely suggestive of the collateral arrangement of the elements 
found in the stem. It is worthy of note that, as shown by Klinge (31), the 
elements of the protoxylem are as a rule neither spiral nor annular, but 
scalariform, reticulate or pitted. 
The phloem is less conspicuously developed, the masses being quite 
small and often but slightly differentiated. In mature roots the elements 
are either partially lignified or considerably crushed by growth pressure. 
It has been shown by Chauvaud (8) that the sieve-tubes are derived in each 
case from a ‘ pericambial ’ cell lying next to the endodermis. The phloem 
is separated from the xylem by a few or sometimes numerous rows of 
usually somewhat sclerotic parenchyma-cells. 
The cortex of the young root consists of many layers of thin- walled 
cells arranged with great regularity in radial rows. In mature roots this 
regularity of structure is usually wanting, owing to the presence of large 
air-chambers in the cortex, separated by very thin radial plates of cells. 
This feature is especially conspicuous in sedges of aquatic or limicolous 
habit. The piliferous layer is not specially modified, and is usually 
B 2 
