Igo BOTANICAL GAZETTE [MARCH 
stems are large in diameter or small determine in the same way the 
number of the strands of the leaf. Such variations may be con- 
sidered as produced directly by growth conditions and therefore of 
physiological interest only. 
The variability in the connection of the stem stele with that of 
the root is related to the position in which the bud develops; thus, 
the bud which developed the stem stele shown in fig. 7 was located 
directly over one of the protoxylem strands of the root, while that 
of the specimen shown in fig. 8 was placed midway between two 
such strands. In the same way, the condition represented in fig. 9 
may be ascribed to a more gradual divergence of the root and stem 
axes; for a time, the two apical cells formed a common tissue within 
which a single stele was developed, as in fig. ro. When the angle be- 
tween the two axes became greater, separate steles were developed. 
It is of course impossible to say what determines these relations 
of position of the protoxylem strands and the stem meristem, oF 
the rate of divergence of the two axes; but it seems evident from 
these variations that the manner of development of the stem stele 
in a bud is controlled by chance or external conditions. Hence 
we may conclude that the stelar characters shown in the develop- 
ment from buds cannot be used in any discussion of phylogeny: 
It is to be noted, however, that two features are constant; these 
are the collateral arrangement of the stelar elements and the endarch 
position of the protoxylem. 
The occurrence of occasional strands of xylem in the pith is a 
feature that is unique, so far as the writer is aware. The manner 
of origin of these strands and their behavior suggests somewhat 
the medullary strands of Marattia; but the absence of phloem dis- 
tinguishes sharply between the two cases. In any consideration of 
this feature it should be borne in mind that these strands occur t0 
any considerable extent in only a single specimen. 
LANG (5) from a study of Botrychium Lunaria has concluded 
that the pith of Ophioglossaceae is purely intrastelar in origin. 
This opinion is based in part upon the occurrence of scattered tra- 
cheids in the pith, particularly in injured rhizomes; this formation 
of xylem elements from parenchymatous cells of the pith is con- 
sidered strong evidence of the stelar origin of the pith. The medul- 
