See 
1901] ANATOMY OF THE OSMUNDACEAE 387 
parenchymatous cell is found among the tracheids. A transverse 
section shows, as mentioned before, a ring of variously shaped 
bundles; and by tracing these up and down, or by boiling a piece 
of stem in potash and then removing the softer tissues, there is 
shown to be a network forming the wall of a hollow cylinder, the 
strands being the “bundles” of DeBary, and the meshes the 
Spaces occupied by the “ medullary rays.” Though there is a 
great deal of regularity in the apparent construction of this net- 
work, as proved by DeBary and Zenetti in O. regalis, yet a study 
of development shows that the “bundle theory” is inadequate 
for giving the right conception of the vascular system. In the 
young stem of the Osmundaceae the wood forms a completely 
closed cylinder, and Van Tieghem, basing his conclusions on 
Todea and QO. vegalts, has stated this to be the case for the 
Whole family. I am able to state that the phenomena in the 
young stem of O. cinnamomea and O. Claytoniana are in accord- 
ance with his general conclusions in this respect. 
Now directly above the point at which a leaf trace leaves the 
stele the wood is not developed for some distance. This gap is 
filled by parenchyma chiefly, except at the outer part, which is 
occupied by sieve tubes. There are exceptions in O. cinnamomea 
to be described later. Thus a transverse section of the stele, 
just above a node, shows a ring of wood broken at one place, 
the break being occupied by the tissues just referred to; in other 
words, the stele here has one medullary ray. fig. 23 shows a 
transverse section of the stem of QO. Claytoniana through this 
region. Still further up the internode the ring is complete 
again. There is the same sort of gap above the second node. 
However, as the nodes become more frequent, that is, as the 
internodes become shorter, a leaf gap extends through more than 
One internode, and in a transverse section there is more than one 
medullary ray, until in the full grown stem, where a leaf gap 
extends through several internodes, a transverse section shows 
Several gaps cut across, or in other words shows several medul- 
lary rays. It is therefore evident that the number of medullary 
rays seen in any transverse section depends on the frequency of 
