1901 | ANATOMY OF THE OSMUNDACEAE 395 
O. Claytoniana, there is but a single layer. Opposite outgoing 
leaf traces the sheath is reduced to a single stratum. 
The metaphloem forms a hollow cylinder consisting of large 
sieve tubes such as have already been described. They are 
thin-walled, and especially in O. regalis in the older parts of the 
stem have often collapsed. The sheath is one or two cells thick 
Opposite the strands of xylem, and several cells in thickness 
opposite the medullary rays (fig. 8, ph). Most of the tubes run 
parallel with the long axis of the stem, but here and there 
“quergestreckte’’ examples occur. 
This cylinder of metaphloem has a smooth outer surface, but 
the inner surface is rendered very uneven on account of the 
wedge-like proliferations of the sieve tissue opposite the leaf 
8aps. Since this is a phenomenon common to all the species 
Studied, we naturally seek an explanation of this peculiar dis- 
position of the phloem. In his memoir on sieve tubes Janczew- 
ski,” who could hardly have been prejudiced by any stelar 
theories, noted that isolated sieve tubes occur occasionally here 
and there in the medullary rays of O. rvegalis. The writer has 
found undoubted cases of the same thing in O. cinnamomea. 
Two such eminent botanists as DeBary and Strasburger have 
disagreed as to the topographical distribution of the layer of 
metaphloem sieve tubes in QO. regal’s. The former states that 
the sheath is continuous, while the latter states that he puts 
himself in Opposition to DeBary on this point, for he considers 
the phloem to be interrupted opposite the medullary rays. 
Strasburger does not say for what reason he considers the cells 
Opposite the medullary rays not to be sieve tubes, My own 
observations on OQ. regalis are precisely in accord with those of 
DeBary and Janczewski. The cells opposite the medullary rays 
differ in no way from the sieve tubes opposite the xylem strands. 
I have found the same to be true of the other species studied, 
With the additional observation that isolated sieve tubes occur 
Sometimes in the tissues filling the leaf gaps of O. cimnamomea. 
* JANCZEWSKI: of. cit. 66. 
* DEBARY: of. cit. 360. 19 STRASBURGER : Of. Cit. 449. 
