250 Lady Isabel Browne. 
Polypodiaceae had not acquired any centrifugal xylem. In the great 
majority of cases the xylem of the two latter orders is endarch, and 
the centripetal wood has been completely replaced by pith, but 
Dipteris, which has been shown to be relatively primitive in many 
ways, retains a certain amount of centripetal wood. The origin of 
the Cyatheaceae and Polypodiaceae from the Gleicheniaceae was 
suggested as early as 1895 by Dr. Campbell (11). 
Some botanists have regarded Matonia as intermediate between 
the Gleicheniaceae and Cyatheaceae, and it has even been included 
in the latter order. Later researches have established its affinity 
with the Gleicheniaceae, but if the Cyatheaceae originated from the 
simplest Gleicheniaceae a common origin for Matonia and the Tree 
Ferns at a relatively not very remote period is assured. The 
occurrence of the Lindsaya- type in the Polypodiaceae, and the close 
affinity between this order and the Cyatheaceae prove that their 
solenostely—even when monocyclic—originated independently of 
the solenostely of Matonia. Professor Bower includes the 
Gleicheniacea e-Matonia-Dipteris series among the few probable 
lines of phyletic origin traced by him. However he does not seem 
to contemplate the origin of Dipteris from Matonia, for he admits 
that, though their vascular systems are of the same type, that of 
Matonia is more complex. Nevertheless, after discussing the 
sporangia of Dipteris and concluding that they resemble those of 
the Cyatheaceae, he claims that the incomplete annulus “points to 
a further departure from the primitive type such as may with 
reasonable probability be found in the sporangia of Matonia and 
ultimately of Gleichenia ” (9). He adds that the anatomy bears out 
this comparison. His researches certainly show that a sorus in 
which the sporangia develop basipetally or without definite succession 
is derived from a sorus in which they originated simultaneously. But 
though in species of Dipteris the sporangia of a sorus may originate 
simultaneously, there is no reason to construct a phyletic line 
passing through the more complex Matonia to Dipteris, for Professor 
Bower has shown that these changes in the construction of the 
sorus have taken place in more than one evolutionary series. 
Dipteris is more primitive than Matonia, not only in the absence of 
any indication of polycycly, but in its mesarchy and in the branching 
of its frond, which appears less specialized than the peculiar branching 
of the frond of Matonia. And lest it should be thought that Dipteris 
might have originated from [simpler extinct Matonineae, we must 
bear in mind that though these may have possessed a mesarch 
