Bower.—Studies in the Phytogeny of the Filicales. VII. 3 
The protostelic state of the adult stem of Lygodium stands alone in the 
family. It may perhaps be correlated with the contracted vascular supply 
to the leaf. 1 Other genera illustrate more advanced vascular conditions. It 
has been shown by Boodle for Schizaea pusilla and dichotoma that the 
young plant starts from protostely, but it soon advances to the condition of 
a medullated monostele. 2 In the former species it is not recorded as 
advancing farther, and Boodle specially states 3 that the central parenchyma 
‘ gives no indication of being of the nature of phloem ’. The same has been 
seen to be the case with 5 . rupestris , which I collected in Australia (Fig. 1). 
This medullated protostele is completely shut in by the endodermis, which 
is unbroken even where a leaf-trace is given off (Fig. 2). 
Fig. 1. Transverse section of the stele of Fig. 2. Ditto, at a point of departure of 
an adult axis of Schizaea rupestris , showing con- a leaf-trace upwards, and of a root-trace di- 
tinuous xylem round a central parenchymatous rected to the left, (x 75.) 
pith. (X75.) 
But while in S.pusilla and rupestris , and apparently also in S. fistulosa? 
there is, so far as described, no advance beyond the medullated protostele, 
other species show an internal endodermis, which may intrude downwards 
as a pouch or pocket from the foliar gaps, but always without internal 
phloem. This leads to more or less complete * ectophloic siphonostely’, as 
in .S. dichotoma? and less perfectly in S. malaccana. 6 The imperfection of 
the ‘ siphonostely * in the last species has suggested two theoretical explana¬ 
tions. 7 Either that it is reduced, and the imperfect siphonostely is vestigial; 
or that the structure is an advance on the medullated protostele, and that, 
1 See Gwynne-Vaughan, Ann. of Bot., vol. xxx, 1916, p. 495. 
2 Ann. of Bot., vol. xvii, Fig. 26, p. 525. 3 1 . c., p. 524. 
4 Boodle, Ann. of Bot., vol. xv, p. 376. 5 Boodle, 1 . c., p. 535. 
6 Tansley and Chick, Ann. of Bot., vol. xvii, PI. XXV, Figs. 3, 4, 5. 
7 Tansley and Chick, 1 . c., p. 500. 
