16 Bower.—Studies in the Phytogeny of the Filicales. VII, 
annulus ceases to be so mechanically important as it is in gradate forms like 
Dicksonia, Accordingly the sporangia show varying degrees of obliquity of 
the annulus. The induration stops opposite the insertion of the stalk, and 
frequently the series of its cells is interrupted there. But cases may be 
found where, though the induration stops, the series may still be followed 
complete past the insertion of the stalk (Fig. 14). These facts corre¬ 
spond with what has been seen for Lindsay a repens (Bory), Bedd. 1 In 
a vertical section of a sporangium it may be seen how an indurated cell of 
Fig. 14. i-iv. Sporangia of Lindsaya linearis from various points of view. ( x 125.) 
the annulus may actually project into the substance of the stalk itself 
(Fig. 14, iv). The number of spores in the sporangia of L. linearis is 24-32, 
and the form of the spore is tetrahedral. 
Dictyoxiphinm. 
It will be best here to introduce that rare monotypic Fern, Dictyo- 
xiphium panamense , Hk., first collected by Camming on the Isthmus of 
Panama, and figured by Sir W. Hooker, 2 who compared the sorus with 
that of Lindsaya . 3 It is a Fern with habit like a large Vittaria, having 
long lanceolate leaves narrowing at the distal fertile region, where a con¬ 
tinuous sorus occupies each margin. The structure of the sorus is not very 
accurately rendered by Bauer in Hooker’s plate quoted above, nor yet by 
the drawings of sections quoted by Diels from Mettenius. 4 Preparations 
were therefore made from herbarium material in Glasgow University, from 
which Fig. 15 has been drawn. This shows that the inner or lower 
indusium (abaxial) is fully developed and curving upwards envelops the 
receptacle while young. But the uppeUor outer indusium ( adax ), which in 
Lindsaya is the more massive, is here absent. It has been seen that the 
1 Studies, III. Ann. of Bot., vol. xxvii, p. 460, Fig. 22. 2 Genera Filicum, Tab. LXII. 
8 Syn. Fil., p. 113. 4 E. and P., i. 4, Fig. 119, B, c. 
