Hymenophyllaceae , Schizaeaceae and Gleicheniaceae. 527 
in the pith of the supposed seedling-plants of S> dichotoma . 
These facts do not suggest a solenostelic ancestry for Sckizaea, 
nor derivation from the Lindsay a- type. 
The first two petiolar bundles are collateral ; hence there is 
no ontogenetic evidence for the petiolar bundles of Sckizaea 
being reduced from the concentric type, and this fact favours 
the conclusion that the stem-structure has not been derived 
from a solenostelic type. 
If one brings the supposed seedlings of dichotoma into 
consideration, the early appearance in them of small endodermal 
pockets and of rudiments which may represent an inner endo- 
dermis, while internal phloem is absent, would favour the 
view of reduction from ectophloic phyllosiphony. 
Ontogeny and Structure of Mature Plant. 
The structure of the young plant of Sckizaea has been 
insufficiently examined owing to lack of material, but such 
data as were obtained, are in agreement with the view derived 
from a consideration of the typical mature structure together 
with its variations in dichotoma. This is stated before 
giving an opinion as to what relative importance should be 
attached to different kinds of evidence. 
A few words may now be said on this subject. Firstly, 
a study of the development of the tissues from the apical 
region, as Schoute (’02, p. 90 et seq.) has shown, does not give 
a morphological criterion. Secondly, the structure of the 
seedling-stem may give a clue to the phylogenetic origin 
of the mature structure, but probably what is found in the 
seedling requires great care in interpretation. Assuming that 
the transitional region of the stem repeats to some extent the 
phylogenetic history of the mature structure, it is extremely 
likely that there may be disturbing factors, which would at 
times make the evidence quite misleading. Thus certain 
kinds of reduction in the structure of the mature stem might 
be attained by one of the stages of the transitional region 
being continued unchanged in the mature stem, so that the 
plant would be a kind of permanently embryonic form 
