4 Plowman . — The Comparative Anatomy and 
strengthened by a narrow hypodermal zone of more or less sclerotic 
mechanical tissue. Tannin-sacs are of quite common occurrence in all 
parts of the root. 
The primary root arises from the micropylar end of the protocaulome. 
It is of relatively short duration and little importance. Secondary roots 
arise endogenously from the rhizome. Rootlets are derived from the 
rhizogenous pericambium situated just within the endodermal sheath. It 
is a well-known fact that in the Gramineae this pericambial sheath is in- 
terrupted at the xylem plates, which lie in actual contact with the en- 
dodermis. The earlier investigators believed the grasses to be altogether 
unique in this respect, all other Monocotyledons as far as studied showing 
a continuous rhizogenous zone. An uninterrupted pericambium has been 
demonstrated by Van Tieghem (54) in species of Carex and Cyperus^ and 
more recently by Holm (25) in Carex Fraseri. However, later studies by 
Van Tieghem and Douliot (58), De Bary (12), and Klinge (31), reveal the 
interesting fact that the majority of the Cyperaceae resemble the Gramineae 
in the possession of an interrupted rhizogenous pericambium, while a few 
species have a uniform, continuous pericambial sheath, and still other 
species show various stages intermediate between these two conditions. 
Consequently there are two types of origin of rootlets. In the majority of 
cases, where the rhizogenous zone is interrupted by the smaller xylem- 
elements, the rootlet is inserted opposite a phloem-strand, and the xylem- 
elements are derived from the two adjacent xylem-strands, so that the oval 
base of origin of the rootlet has its longer axis transverse to the main axis 
of the parent root. On the other hand, in those cases in which the peri- 
cambium is continuous the rootlets are inserted directly upon the xylem- 
strands, each rootlet connected with but a single strand, and having the 
longer axis of its oval base of attachment parallel to the main axis of the 
parent root. 
These facts have a certain interest from their bearing upon the 
relationships of grasses and sedges as expressed by Van Tieghem (56) and 
others, and to be considered more fully on a subsequent page. In its 
apical development the root presents no features uncommon to the great 
majority of the Monocotyledons. As shown by De Bary (12), Van 
Tieghem (56), Treub (53), and others, the root-cap is developed from a 
distinct calyptrogenic initial meristem, outside and independent of the 
dermatogen, so that the piliferous layer presents a smooth contour, traceable 
under the root-cap quite to the initial region. 
The Rhizome. 
The great majority of the Cyperaceae grow by a perennial root-stock, 
which is in some cases long and slender, in other cases extremely short 
and compact, while other members of the Order present all intermediate 
