6 Plowman. — The Comparative Anatomy and 
in the rhizome of the Cyperaceae. It is found in especially great quantities 
in Scirpus robustus and 5. americanus , and in the tuberous rhizomes of 
many species of Cyperus. 
It has been found that outside the central cylinder all of the characters 
are more or less highly susceptible to the influence of environment, often 
presenting a considerable range of variation within the same species, and 
consequently possessing comparatively little value from a phylogenetic 
point of view. Accordingly our attention will be directed more specifically 
toward the characters of the central cylinder itself. 
In the seedlings of Scirpus microcarpus the central cylinder presents 
a condition of affairs strikingly similar to that described and figured by 
Chrysler (9) for Smilacina , the only difference being found in the somewhat 
more numerous leaf-gaps and in the earlier appearance of numerous medul- 
lary strands, which, however, are almost without exception of the collateral 
type. Young plants of other species indicate a similar tubular condition 
of the central cylinder in its earlier stages, followed in later development 
by the appearance of medullary strands, which in the majority of the 
Cyperaceae are of the concentric type. Thus it appears from a cursory 
glance at the seedling of the Cyperaceae that the central cylinder in its 
earliest stages is a simple siphonostele of the phyllosiphonic type, similar in 
every essential particular to that of the Dicotyledons. Only in later stages 
of growth does one find a highly complicated arrangement of stelar struc- 
ture. It seems very desirable that the developmental history of the 
Cyperaceae should be more thoroughly studied. 
The central cylinder of the mature rhizome may be described under 
two fairly well-marked general types, which are characterized by the 
disposition of the xylem-elements of the fibro-vascular bundles. In the 
first of these types, which is by far the more common among the Cyperaceae, 
all or most of the bundles are of the concentric sort, with the xylem distri- 
buted more or less uniformly all around the phloem. To such bundles the 
term ‘ amphivasal 5 has been very generally applied, and those Cyperaceae 
which present this type of rhizome bundle may, for purposes of description, 
be grouped together as the Amphivasae. Here belong most species of 
Scirpus , Cyperus , Eleocharis , Eriophorum , Rhynchospora , and Car ex. In 
certain other forms, notably Didichium , Cladium , Scirpus microcarpus , 
Y. americanus , Y. robustus , &c., the bundles are of the simple collateral 
type, with the relatively few xylem-elements disposed on the centripetal 
side of the bundle. Those forms which present this arrangement may 
be termed the Centrivasae. 
Scirpus cyperinus will serve as an example of the Amphivasae. 
A part of the central cylinder of this species is shown in PI. I, Fig. 3 , 
and a part more highly magnified in Fig. 4 . It will be observed that 
the bundles are very numerous and almost exclusively of the amphivasal 
