412 BOTANICAL GAZETTE [DECEMBER 
the medullary rays, the occasional presence of sieve tubes in the 
medullary rays, the fact of the internal phloem, the connection 
of medulla and cortex through ramular and foliar gaps, the 
presence of sclerenchyma in the medulla, the bending out of the 
internal endodermis into the leaf gaps, and the facts of develop- 
ment, all become intelligible. 
Fourth, which of the species studied possesses the most prim- 
itive type of central cylinder ? 
After a fairly comprehensive study there is one feature that 
stands out prominently, the great similarity and uniformity of 
vascular structure in the various species of Osmunda and Todea. 
According to Solms-Laubach the stems of fossil remains of this 
family, of which none earlier than the Tertiary have been found, 
do not present any striking differences from the living represen- 
tatives. Paleobotany, therefore, offers no solution to the prob- 
lem. In spite of the conservatism of the central cylinder, there 
are, however, minor anatomical differences. On the basis of 
these alone, without referring to the young sporophytes, I think 
there is sufficient warrant for placing O. cénnamomea at one end 
of the series, possessing as it does an internal endodermis, inter- 
nal phloem, and wide ramular gaps. It is difficult to say which 
species is to be placed at the other end of the series. In view 
of the fact that O. Claytoniana never has sclerenchyma in the. 
medulla, that there are small or even no ramular gaps, no inter- 
nal sclerenchyma, and even a degenerated external endodermis, 
we may not be far astray in putting it in. the position farthest 
from O. cinnamomea.. Now of these two, which retains a cen- 
tral cylinder more nearly primitive? If O. regalis has a medul- 
lated monostelic central cylinder, as has hitherto been claimed 
for it, then O. Claytoniana has also, and therefore, according to 
Van Tieghem, a more primitive form than that of O. cimmamomed. 
Assuming the correctness of this for the moment, it will be in 
order next to see if such phenomena as presented by 0. cinna- 
momea could be derived according to Van Tieghem’s hypothesis 
from such a simple medullated monostelic form as that of 0. 
Claytoniana. 
