ene 
1907] HOLM—RUELLIA AND DIANTHERA 309 
the Acanthaceae, since it is so very rare among dicotyledonous 
plants, being known only in Nymphaea, Gunnera, Primula (AURIC- 
ULA), and Pinguicula. In polystelic axes, as described by VAN 
TrecHEM and Douvtior,‘ each stele has its own pith, parenchymatic 
Tays, mestome, and endodermis, and they are all surrounded by a 
common cortical parenchyma. When the mestome (leptome and 
hadrome) is distributed in the axis as several isolated strands, and of 
mestome alone, such structure is called by the same authors astelic; 
a structure known in Anemone, Ranunculus, Ficaria, Caltha, Hydro- 
cleis, etc. 
In Dianthera the steles are very distinct and readily to be recog- 
nized as such, since they are cylindric and possess all the necessary 
elements. In comparing Ruellia, which is a land plant, with the 
aquatic Dianthera, they are found to be very different, and it is 
interesting to notice in the latter the combination of characters 
peculiar to aquatic plants in general and others peculiar to Acan- 
thaceae. 
Ruellia ciliosa Pursh. 
A woodland type from open woods and thickets, associated with 
Siphium trijoliatum, Salvia lyrata, Galactia pilosa, etc. The stem 
above ground dies off in the late autumn (November) and the buds 
- that winter over are subterranean. The rhizome, which persists for 
several years, is creeping and horizontal, or sometimes ascending; 
the horizontal direction I believe is most typical of the species, and 
in this the internodes are very short and almost concealed by the 
numerous thick roots. When the rhizome is ascending, the inter- 
nodes are more or less stretched and readily visible. The leaves of 
the rhizome are very short, scale-like, and membranaceous. Several 
axillary buds are to be observed on the rhizome; in the larger of 
these, two or three internodes are frequently so distinct that the 
term shoots might be more correctly applied to these than buds; 
however, they remain underground during the winter. 
The branching of the rhizome is sympodial, and very regularly 
So, even in old specimens. The apical internode terminates in an 
aerial shoot, which dies down to the ground at the close of the season, 
and the continued growth of the rhizome is secured by the develop- 
+ Sur la polystélie. Ann. Sci. Nat. Bot. VII. 3:275. 
