53 
Inter-relationships of the Phyla. 
(except perhaps in certain roots) there is no sharp delimitation of 
morphologically distinct tissues at the meristem (32). Professor 
Bovver (10) and Dr. Jeffrey (21) also hold the view that apical 
segmentation affords no proof of the morphological nature of a 
tissue. 
Much discussion has centred round the primitive microphylly 
or megaphylly of the phyla. In 1903 Dr. Jeffrey suggested a 
division of the Pteridophyta into Pteropsida (including the Ferns) 
(20) and Lycopsida (including the Equisetales, Lycopodiales and 
Psilotales). The Pteropsida, though distinguished also by other 
characters, were regarded as palingenetically megaphyllous and the 
Lycopsida as palingenetically microphyllous ; it was asserted that in 
the former the departing leaf-trace left a gap in the stele, while in 
the latter the gaps in the stele were ramular (20). In 1903 Professor 
Lignier brought forward good evidence that the numerous simple 
leaves of Catamites and of species of Sphenophyllum represent the 
ultimate lobes of a smaller number of compound leaves found in 
Archceocalamites and other species of Sphenophyllum, and that these 
smaller-leaved forms are descended from species with fewer and 
compound leaves (28). Dr. Scott, in 1907, accepted this view (34). 
But Professor Lignier did not extend his explanation of the origin 
of microphylly in the Sphenophyllales and Equisetales to the 
Lycopodiales and Psilotales, he asserted that these forms were 
primitively microphyllous, and that their small leaves, termed by 
him phylloids, were not homologous with the large leaves of Spheno¬ 
phyllales, Horsetails and Ferns which alone he regarded as true 
leaves (28). This view seems utterly untenable for the Psilotales, 
for Dr. Scott and Professor Thomas have practically established 
the affinity of these plants with the Sphenophyllales (33), (34), (42), 
proved by Professor Lignier himself to be primitively megaphyllous. 
Recent work has shown that the double foliar bundle was no 
peculiarity of Sigillariopsis but probably characteristic of the 
Sigillariae generally (1), (24), and if Professor Lignier’s contention 
(in a recent re-statement of his views) that the phylloid as opposed 
to the true leaf is always unifascicular, and that bifascicular 
foliaceous emergences are always reduced leaves or lobes of leaves 
(29) be accepted, then the phylloid theory of Lycopod leaves falls 
to the ground also. But though this makes it tempting to regard 
the leaves of Lycopods as reduced, we must remember that the 
unifascicular leaf of Lepidodendron is older than the bifascicular 
one of Si gill aria. 
