580 
DR JOHN M‘LEAN THOMPSON ON 
found at the present time in the young individual when it is absent in the adult. 
( Ophioglossaceee , Equisetacese, Ranunculacese.) The pith must in all cases he 
regarded as a derivative of the cortex, which has become more or less completely 
segregated within the stele." These remarks contain no actual reference to 
Platyzoma, but according to their conclusion the pith of Platyzoma must be 
regarded by Dr Jeffrey as of extrastelar origin, and the stele itself as reduced so 
as to have lost internal phloem and leaf-gaps, but still to have retained its inner 
endodermis. 
I have dwelt on the published statements of those who have supported the 
reduction theory for the stele of Platyzoma so that the arguments involved might 
be fully understood. By reiteration rather than the support of cogent facts they 
have been strengthened, but they have not solved the stelar problem. I am driven 
to the conclusion that the reduction theory as so far stated stands merely upon 
unwarranted and comprehensive assumptions, and that there is no justification in 
the recorded facts of fern-anatomy for regarding the reduction hypothesis for 
Platyzoma as anything more than an undemonstrated possibility. Having regard 
to the recorded facts, I am constrained to maintain this position with regard to the 
stelar morphology of Platyzoma in direct opposition to Dr Jeffrey’s recent state- 
ment that, “ so far as the plentiful evidence in the case of the Filicales is concerned, 
it seems beyond reasonable doubt that the median parenchyma of the tubular or 
siphonostelic central cylinder has come from the outside, and is not the result of 
internal differentiation within the stele” (12). 
But the object of this paper is not mere criticism of the theoretical statements 
which have grown around a limited body of fact. It is rather the recognition 
of the problems of stelar structure which await solution for Platyzoma, and the 
contribution and employment of certain new facts which have emerged from recent 
investigation. It was evident from the outset that the facts obtained from a few 
sections of the stem and from the general habit of this plant were totally inadequate 
to allow of a confident opinion as to the true nature and origin of the tubular stelar 
structure. Ample material embracing “sporeling” stages and mature plants could 
alone provide the fuller ontogenetic facts which are necessary. The “sporeling” 
stages have not yet been obtained, but through the kindness of Dr Bailey of 
Brisbane Botanic Gardens a number of plants of various ages have been available 
for study. In most cases the stem was robust, and, though basally incomplete, 
measured from three to five inches in length. In all of them the apparent zonation 
of leaves already described was seen, and all were heterophyllic (5), (13). The 
majority of the larger stems were dichotomously branched, and in one instance the 
branching had occurred at least twice. The materials included one small and 
apparently relatively young plant. Its stem was more slender than that of any of 
the larger specimens. Basally it was incomplete, but otherwise it was a perfect 
specimen. It showed well the leaf-zonation, there being three groups of pinnate 
