AND THEIR BEARING ON STELAR THEORIES FOR THE FERNS. 
7 25 
— is 
n 
and results from the following steps. Inner endodermal cells appear in the pith 
(En.', fig. 28). These mark the base of a tube of inner endodermis closed below and 
widening upwards in the pith (En., text-fig. 3). It is 
continuous on the one hand with the endodermis of the " 
next departing leaf-trace (k), and thus provides the 
increase of endodermal area which an axillary pocket 
would secure. It is continued as the inner endodermis 
lining the internode immediately above (text-fig. 3 ; and 
En/, fig. 29). In this figure is shown the stelar structure 
slightly above the point of departure of leaf-trace k. 
That the tissue which this inner endodermis involves 
(M, fig. 29) is histologically similar to the inner cortex is 
matter for no surprise, for they are continuous through a 
stelar gap and act as one tissue. The stelar structure 
thus attained is in fact solenostelic. This will be further 
apparent from fig. 30, which represents a transverse section 
of the stele at IV (text-fig. 3) after the first leaf-gap is 
closed. The medulla (M), inner endodermis (En/), inner 
phloem (Ph/), xylem-cy finder (X), outer phloem (Ph.), and ^ 
outer endodermis (En.) are all shown. Followed upwards, 
the inner endodermis is continuous with the endodermis 
surrounding the next succeeding leaf-trace (L, text-fig. 3). 
In this way the solenostelic structure, once secured, is 
maintained. 
Thus it has been shown that, as in Schizsea malaccana, 
Schizsea dichotoma, and others, so also in Gleichenia 
pectinata, medullation and pocketing are distinct pheno- 
mena. That medullation antedates pocketing in the 
ontogeny has indeed been demonstrated. There is no 
structural evidence of intrusion or flow of cortical tissue 
by which the pith of the solenostelic tract might arise, I 
and study of the growing point itself supports the view 
that by change of procambial destination the stelar changes 
here described are effected. By such a static change alone 
the continuity of endodermis across the pith could be 
secured while solenostely is maintained. This formation 
of inner endodermis follows upon the interruption of the 
stelar xylem above a leaf- trace (text-fig. 3), which is thus 
the first associated with a true foliar gap. The immediate 
result of these changes is the physiological delimitation of the stelar pith of the 
protostele below the inner endodermis from the later formed pith of the solenostelic 
f 
J 
I 
Text-fig. 3. 
