THE MORPHOLOGY OF THE STELE OF PLATYZOMA MICROPHYLLUM, R. BR. 581 
leaves alternating with zones in which filiform leaves predominated. The stem of 
this small plant and those of a number of the larger specimens have been sectioned 
throughout their entire length, so that no opportunity might be lost of discovering 
in them a solenostelic condition, foliar gaps, or evidence of the loss of gaps and 
internal phloem. The discovery of any one of these would materially affect any 
interpretation of the stelar state. Degenerate gaps and phloem would undoubtedly 
raise the reduction theory to the plane of probability, but an actual solenostely 
without evidence of degeneration or reduction would be open to interpretation as 
the result of stelar amplification, provided an upward progression from protostely 
to this hind of tubular stele could be indicated in the ontogeny. But in any case, 
neither the presence of degenerate leaf-gaps and phloem, nor the existence of the 
so-called ectophloic-siphonostelic state, would provide any grounds for a belief in 
the cortical origin of the pith of Platyzoma. At most they would have demon- 
strated merely a connection between pith and cortex which would seem to have 
been broken frequently in the phyletic sense in this plant. 
On the other hand, the discovery of a protostelic state giving place in the 
ontogeny to a well-defined medullated protostele with isolated internal endodermis 
and entire absence of foliar gaps and internal phloem would lend support to the 
theory of upgrade development, unless it be further assumed, without evidence 
from fern-anatomy , that such a protostele merely demonstrates the extent to which 
reduction may go. Such a view of widespread reduction would necessitate that the 
internal endodermis had followed the inner phloem and the leaf-gaps “ into 
oblivion,” with the result that a stelar structure in no way distinguishable from 
an original protostele was established. The supporter of such a reduction theory 
would be compelled to view with suspicion most fern-protosteles, for each would be 
open to interpretation as the result of drastic reduction from a solenostelic state 
or from some other type of tubular stele. The “ sporeling ’’-structure of modern 
ferns — in which protostely so commonly figures — would likewise be placed under 
suspicion as a possible reduction phenomenon. The logical conclusions to such an 
attitude would be, first, to suspect everything with a pure protostele or a medullated 
protostele of being reduced ; second, to negative ontogeny unless it shows through- 
out a solenostele or some upgrade modification thereof ; * and third, to consider 
solenostely and not protostely as primitive in the sense recently advocated by Di- 
Jeffrey, “that the tubular condition is both typical and primitive for the ferns 
in general, with the sole exception of those forms in which the organisation of the 
stele maintains the original protostelic state ” (14). This would imply that protostely 
must persist throughout the entire ontogeny if it is to be considered an original 
protostely, and that once solenostely appeared, the original protostely was lost, and 
that where protostely and solenostely exist in the same individual, the latter is the 
* In discussing the stele of Angiopteris evecta in 1902 (8), Dr Jeffrey stated that he had examined some young 
plants, but “ unfortunately these proved rather too young for the present purpose, since the central cylinder had as yet 
hardly passed into the tubular condition .” 
