THE ANATOMY AND AFFINITY OF STROM ATOPTERIS MONILIFORMIS, METT. 143 
narrow elements bear multiseriate pits, and are not to be confounded with spiral 
protoxylems, and indeed, as has already been stated, spiral protoxylems are absent 
from the upright portion of the stem. Their absence is undoubtedly due to slow 
differentiation or only slight extension during the development of the stele. But 
although the absence of spiral protoxylems in the erect branch of Stromatopteris 
prevents comparison with the mesarch protoxylems of Gleichenia, it in no way 
militates against a G-leicheniaceous affinity for Stromatopteris. In fact, in possessing 
a protostelic axis, Stromatopteris is well in line with the majority of the Gleicheniaceae, 
and differs in this respect only with Platyzoma and Gl. pectinata ■ The former 
possesses a medullated protostele with internal phloem, the latter a solenostele. 
In the plant which has been under discussion the basal sections of the stem show 
the stele in process of division. The xylem is divided into two similar though some- 
what unequal masses separated by a zone of parenchyma. The phloem is divided 
into two arcs, the margins of which are passing into the separating zone of parenchyma, 
and are about to extend so as to completely invest the xylem-groups (fig. l). 
When division is completed the stele is divided into two similar parts (fig. 2). Of 
these the right-hand member passes directly into the broken branch, while the left 
is continued into the deflected stem. 
A comparison of the form of our plant with the specimen in Edinburgh Herbarium, 
and the figures and descriptions referred to, strengthens the opinion that the broken 
branch which was thus supplied with a protostele was of axial nature. 
As the left branch is ascended its stele widens and prepares to divide (fig. 3). 
The division of the stele which now follows and which precedes the wide forking of 
the axis is an unequal one (fig. 4). The xylem of the left stele is wide and 
parenchymatous, while that of the right is condensed and slender. The condensed 
form of the latter is not, however, long maintained, and within ^ inch from the 
point of branching the right-hand stele has become elliptical in section and 
parenchymatous, and is already preparing for a new and final division (fig. 5). This 
latter division is noteworthy. It results in the formation of two steles of about 
equal diameter (fig. 6) ; but while the xylem of the left-hand stele thus formed is an 
almost solid mass of tracheides, and is surrounded by phloem of uniform thickness, 
the xylem of the right-hand stele is crescentric in section, and the phloem is then 
opposite the parenchymatous bay. The solid protostele supplies the short conical 
branch, while the stele with the crescentric xylem passes on into the base of the 
apparently petiolar branch. Throughout the length of this short, conical, and 
almost horizontal branch, the protostelic state is maintained, the xylem becomes 
more parenchymatous (fig. 7), and, towards the very tip of the stele, becomes 
very reduced in bulk (fig. 8) before ending abruptly in an apical mass of 
undifferentiated cells. 
. As to the meristele entering the branch which may be held as petiolar, it will 
suffice to state that within the cylindrical basal portion of the branch the stele first 
