45 
Anatomy of the Ophioglossaceae . III. 
importance as affording a simple expression of the double leaf-trace which 
assumes such complicated forms in the petioles of the Zygopterideae. If 
the origin of the trace of Clepsydropsis itself, as described by Bertrand, be 
included in the comparison, we can contemplate a preceding stage in which 
the xylem of the departing trace includes a single protoxylem. In any 
case this monarch stage is realized in Thamnopteris , and may be spoken of 
as the pre-clepsydroid stage. 
Dr. Bertrands interpretation of these structures differs considerably 
from that of Kidston and Gwynne-Vaughan. 1 The essential point for our 
purpose is brought out by the nomenclature used by the former investigator, 
who describes all these traces as 4 divergeants fermes \ This idea of a closed 
divergent appears to imply that the outer xylem of the trace is completed 
adaxially. It may or may not include a portion of the mixed pith or inner 
xylem, but except in so far as it does this it is not mesarch in the sense in 
which this term applies to the stelar tube of Helminthostachys , i. e. as being 
composed of outer and inner xylem. This conception of a closed divergent 
plays an important part in the detailed accounts of Fern anatomy by 
Bertrand and Cornaille, and has recently been more directly applied to the 
Cycadofilices by Chodat. The clepsydroid stage is on this view naturally 
regarded as composed of two closed divergents. 
While the other Ophioglossaceae 2 have leaf-traces that are most readily 
compared with the C-shaped trace of many recent Ferns, Helminthostachys 
in the variety of its leaf-trace departure comes into line with the plants 
referred to above. As has been shown in the detailed descriptive account, 
its leaf-trace exhibits every degree of adaxial completion of the arc of outer 
xylem with which it is continuous in the stem. It goes far to justify the 
conception of the closed divergent as distinct from the mesarchy exhibited 
by the stelar tube of xylem. The inner xylem may or may not extend for 
some distance into the departing trace, being included within the closed 
divergents of the pre-clepsydroid or clepsydroid stages. As in the case 
of Ankyropteris , the inner xylem soon disappears from the trace, but its 
presence enables a clear distinction to be drawn between the adaxial com- 
pletion of the xylem of the trace and true mesarchy. There is a striking 
resemblance between the clepsydroid stage of the departing trace in 
Helminthostachys and that in Clepsydropsis and the various Zygopterideae 
mentioned above. The pre-clepsydroid stage in Helminthostachys is com¬ 
parable to the similar monarch stage in Thamnopteris , especially when the 
adaxial completion of the xylem takes place before separation from the 
stelar xylem. 
1 P. Bertrand: Progressus Rei Botan., vol. iv, p. 182; Kidston and Gwynne-Vaughan : 
Proc. R. S. Edinb., vol. xxviii, p. 433, and Trans. R. S. Edinb., vol. xlvi, p. 654, and vol. xlvii, 
pp. 469 ff. 
2 The occasional adaxial completion of the xylem in Botrychium lunaria must be remembered 
in this connexion. Ann. of Bot., xxvii, pp. 223 and 239. 
