408 BOTANICAL GAZETTE [DECEMBER 
the deeply infolded petiolar supply of the cycads in our argument. 
Since the leaf traces of this group originate on the opposite side of 
the stem from that on which they pass out into their corresponding 
leaf, it would be necessary to assume that each half of the leaf 
supply carried with it its own peculiar portion of the medullary 
parenchyma, and that the fractions were accurately joined with 
one another in the leaf base, to the exclusion of the fundamental 
tissue of the cortex, if we were to accept the idea that the fibro- 
vascular tissues are in general unable to embay or include portions 
of the fundamental tissues of the cortex. This seems much too 
improbable a supposition to be seriously entertained. 
It appears evident, since the stelar system of the stem in the 
case of certain of the lower Pteropsida, for example, species of 
Onoclea, Cystopteris, Aneimia, etc., is able to include tissues and 
substances which are beyond question extrastelar in their origin, 
that no difficulty arises in regarding the pith present within the 
siphonostelic central cylinder of the lower (as well as the higher) 
Pteropsida as morphologically equivalent with the fundamental 
tissue of the cortex, with which it is often continuous through the 
gaps in the stelar walls resulting from the exit of the vascular 
supply of leaves and branches. <A further argument in favor of 
this view is the frequent textural similarity between pith and cortex, 
even where the former as the result of upward evolutionary changes 
is no longer continuous with the fundamental tissue without the 
stele. It follows equally that the morphological doctrine for which 
STRASBURGER is responsible, and which has been carried to its 
logical conclusion and reductio ad absurdum by the English anato- 
mists, namely, that the criteria of the morphological status of plant 
tissues are to be derived from a study of the growing point of the 
mature organ rather than from comparative anatomical consider- 
ations and particularly from a study of the seedling, falls to the 
_ ground. 
It is now possible to consider with advantage the alleged primi- 
tive absence of foliar gaps in the Pteropsida, which has recently 
been asserted by GwyNNE-VAUGHAN in connection with studies 
on fossil representatives of the Osmundaceae. In the genus 
Thamnopteris, this author has found the center of the stele to be ; 
