548 Bower, — On the Primary Xyleni , and the 
unites at the leaf-gaps. The question may be raised, What is the real nature 
of that external conjunctive tissue? It is to be noted in Osmunda , as it is 
also in the Ophioglossaceae, that the connexion is not with the parenchyma 
immediately within the endodermis, which might be held to be really 
a sister layer with the endodermis, and so be ultimately cortical in its 
origin ; but with the conjunctive parenchyma internal to the phloem, which 
is truly stelar. This being so, the origin of the whole pith in the Osmun- 
daceous seedling up to the twelfth leaf (and even further, as shown by Faull’s 
drawings, PI. VI, Figs. 13-17) appears to be truly intrastelar, but derived 
partly from intraxylic parenchyma, partly from the conjunctive tissue. 
Divested of all theory, this appears to be the actual fact. 
Faull states specifically (loc. cit., p. 527) that in seedlings of O . cin- 
namomea ‘ internal phloem, and wide open leaf-gaps, through which cortex 
and pith communicate, were not found ’. He goes on to suggest that 4 their 
absence may be indicative of reduction expressed in the seedling stage ’. 
But this seems an unnecessary perversion of the evidence from ontogeny in 
the interests of a favoured theory. It would seem better to question the 
truth of the theory of the reduction of the Osmundaceous vascular system 
from an £ amphiphloic siphonostele ’, than by its acceptance to be driven to 
construct a second hypothesis of ‘ reduction expressed in the seedling stage ’, 
in order to support it. If, however, the up-grade view of the structure of 
the Osmundaceae be accepted, the facts of the ontogeny will be found to 
run parallel with the facts for Botrychium. We may conclude from the 
ontogeny that an intraxylic pith originated first in all these cases, and that 
it is subsequently put into connexion with the conjunctive parenchyma (or 
xylem-sheath) at the gaps in the xylem-ring. 
Further, we may see from Faull’s description of sporelings of Osmunda , 
and less clearly in my weak plants of Botrychium Lunar ia, that the purely 
stelar pith, once established, is liable to be almost or even entirely obliterated 
as it passes upwards, and that it may be again reconstituted, until it finally 
settles down to permanence. This is to be compared with the behaviour 
of the intrastelar pith in the roots of certain Leguminosae, in which 
Flaskaemper was able experimentally to control the disappearance and 
reappearance of pith, and to show that the formation of an intrastelar pith 
depends upon nutrition. 1 
A comparison of the structure of the sporeling in the two families 
suggests an interesting relation of it with the early nutrition. In the 
Osmundaceae the nutrition of the sporeling is by the green prothallus, 
which lives as it were hand to mouth. The sporeling which it produces is 
at first protostelic, and the vascular changes as described by Faull are 
entirely intrastelar for many internodes. In the Ophioglossaceae, on the 
other hand, there is a storage prothallus, which in B. virginianum is of 
1 Flora, 1910, p. 205. 
