Phytogeny of the Cyperaceae . 
9 
the bare of the aerial stem and closely investing the outgoing bundles 
for some distance. This jacket consists of about three layers of somewhat 
elongated, pointed or irregular, thick-walled, profusely pitted cells, of 
a more or less tracheidal appearance, with the longer axis radially disposed, 
and arranged in a dense zone bordering directly upon the outside of a little- 
differentiated endodermis. This peculiar sheath is apparently unique, and 
duplicated in no other species in the entire Order. 
The accompanying Table I presents in concise form the more salient 
features of the rhizome in the more interesting species studied. Besides 
the species named in the table, some twenty other Carices have been 
examined, together with a few additional species of Scirpus , Eleocharis , and 
Fimbristylis. For purposes of confirmation and comparison, a study has 
been made of species of J uncus , Streptopus , Pontederia , various grasses, &c. 
The more striking features of the rhizome of the Cyperaceae may be 
summarized briefly in the following key, based chiefly upon the generic 
characters of the central cylinder. 
Generic Key to the Cyperaceae. 
I. Centrivasae. Bundles of the rhizome collateral, or rarely amphivasal 
at the periphery. 
1. Medulla cavernous. 
a. Endodermis and peridesm conspicuously sclerotic 
b. Endodermis and peridesm not sclerified . . . . 
2. Medulla not cavernous. 
a. Endodermis not apparent ..... 
b. Endodermis distinct. 
aa. Simple, medulla thin-walled ..... 
bb. With sclerotic medulla ..... 
cc. With external sclerotic zone continuous across base 
Dulichiuni. 
. Cladium , 
Scirpus microcarpus . 
Scirpns americanns. 
Scirpus robustus. 
of culm ...... 
II. Amphivasae. Bundles of the rhizome all amphivasal. 
1. Peridesm only slightly developed, or undifferentiated. 
a. Medulla aerenchymatous 
b. Medulla compact. 
aa. Rhizome tuberous ..... 
bb. Rhizome not tuberous. 
aaa. Small, bundles few .... 
bbb. Small, bundles many .... 
ccc. Large, bundles very many 
2. Peridesm uniformly well developed. 
a. Rhizome tuberous ...... 
b. Rhizome not tuberous. 
aa. Internodes long, xylem elements large . 
bb. Internodes short, xylem elements small, few 
Scirpus fluviatilis. 
. Stenophyllus. 
Lipocarpha. 
. Eleocharis. 
. Scleria. 
Cyperus Papyrus. 
. Kyllinga. 
. Carex. 
. Hemicarpha. 
