5 
Phytogeny of the Cyperaceae. 
conditions. Even the annual species commonly preserve the rhizomatous 
habit, the first few internodes of the stem being very short and usually 
growing more or less obliquely in the soil. Indeed, where the rhizomatous 
character of the stem-base is not apparent externally, it is always 
demonstrable from internal structure. 
Frequently the rhizome bears hard, brown leaves of considerable size 
at the nodes, but more generally the leaves are reduced to mere scales. 
After a period of horizontal or oblique growth the rhizome bifurcates to 
give rise to an aerial stem or culm which is commonly leafy, at least at the 
base, and which ultimately bears the inflorescence. Not infrequently 
several aerial axes are given off from the rhizome in a single season’s 
growth, some of them being only vegetative, while others bear both leaves 
and flowers. But it more often happens that the number of aerial shoots 
is very small in each season’s growth, and all of them ultimately develop 
flowers. Fibrous roots are produced in large numbers from the nodes of 
the rhizome. In most cases the elongated rhizomes are not of uniform 
size throughout their length, but consist of swollen nodes and slender 
internodes, as in Scirpus americanus ; or the rhizome may be made up of 
swollen tuberous portions connected by slender internodes, as in Cyperus 
esculent us, and to a less marked degree in Scirpus cyperinus , N. atrovirens , 
N. lineatus , &c. ; only rarely does one find the rhizome of uniform size for 
a considerable part or the whole of its length, as in Scirpus robustus and 
a few of the Carices. 
Internally the rhizome consists of a central cylinder which is very 
rarely hollow in the mature condition, as in Carex scoparia , Cladium 
mariscoidcs , Dulichium arundinaceum , &c., but which as a rule is solid or 
only slightly aerenchymatous, and composed of several to very many fibro- 
vascular bundles embedded in fundamental tissue and surrounded by a 
well-defined endodermal sheath (except in Scirpus microcarpus and Cladium 
mariscoides ), which is either simple or variously reinforced by circular 
fibres or a sclerotic zone. Outside the endodermis is the very variable 
cortex, bounded externally by the epiderm. The cortex may be sclerotic 
in whole or in part, unmodified parenchyma, aerenchymatous in varying 
degree, or even cavernous as in the upper side of the rhizome of Dulichium. 
Bordet (6), Palla (35), and others have attempted to utilize the characters 
of the cortex as diagnostic features of the Cyperaceae, but with very 
doubtful success, owing to the fact that these features are extremely 
variable under change of environment. The peripheral portion of the cortex 
is very generally modified to form a sclerotic hypodermal zone, or at least 
a series of hypodermal ribs, of which the function is clearly mechanical. 
The epidermis is not infrequently sclerotic, and rarely covered with a thick 
cuticle. Tannin-sacs are of common occurrence throughout most rhizomes. 
With a few rare exceptions among the Carices, starch is everywhere present 
