SHOWS MICROPHYLLY TO BE PRIMITIVE 199 
axis is protostelic at the base, and the first leaf-trace may depart without in 
any way altering the structure of this stele, thus showing the cladosiphonic 
character. It is only subsequently, by the overlapping of those intrusive 
pockets of phloem and endodermis which accompany the exit of the leaf- 
trace, that a gradual transition is effected to the 
phyllosiphonic type. Thus the anatomical evidence 
indicates a probability that, even in large-leaved 
Ferns, the cladosiphonic was the primitive type; 
but that the phyllosiphonic, once initiated, is as a 
rule maintained: this is shown by its persistence 
in the Seed-Plants, even where the leaf has been 
reduced in size. Accordingly the trend of ana- 
tomical evidence is towards the recognition of a 
small-leaved, strobiloid type of construction of the 
primitive sporophyte. 
It may be objected that in certain Pteridophytes 
the condition of the embryo is such as to militate 
against any strobiloid theory, and that their ana- 
tomical details offer as great an obstacle as their 
external form. The cases which will be cited are 
those of some Lycopods, in which the first leaves 
are isolated, and show no vascular connection with 
the later-formed leaves (Fig. ror): or my own 
observations on Phylloglossum may be held as a 
valid objection, for there also a single vascular 
strand has been observed passing down in one case 
directly from a protophyll into a root, without any 
relation to the other members.! Such cases may 
be held to establish the individuality of the leaf 
anatomically before the axis has any existence. In 
the interpretation of these the discussion on embry- : 
ology in Chapter XIV. should be recalled, and Hieee 
especially the opinion there brought forward that ‘Aba philecucehan Diaaran 
the separation of individual leaves in certain cases chee ties ee 
from the rest of the shoot is a secondary condition, a eG Ea 
resulting from what might be called anticipatory {hs endodermis is indicated by 
development, to meet an early need for an assimi- ee (After Gwynne- 
latory mechanism. The inconstancy of detail which 
is shown by the embryos of Z. cernuum, and by the young annual growths 
of Phylloglossum, is in itself a support of this opinion. The vascular supply 
of the leaves thus isolated is separated it is true from that of the main 
shoot, but its separateness may be held to be secondary, and not a proper 
basis for conclusions as to the primitive construction of the vascular system 
of the normal shoot. 
1 Phil. Trans., part ii, 1885, Plate 73, Fig. 42a. 
