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1901] ANATOMY OF THE OSMUNDACEAE 389 
The protoxylem occurs in small groups of six to eight cells 
each, and a transverse section of the central cylinder shows from 
five to seven of these groups. Each group of protoxylem 
elements passes out in its entirety into a leaf trace, and on fol- 
lowing back from the leaf trace each vanishes as already 
described. The protoxylem is therefore not continuous through- 
out the stem, but is in small, discontinuous strands. This fact 
has been recorded for O. regalis by Zenetti.™ 
Lying externally to the wood are from four to six layers of 
elongated parenchymatous cells, rich in protoplasmic contents 
and in small starch grains. They are continuous with the 
parenchymatous cells of the medullary rays and do not mate- 
tially differ from them. Those occupying the middle of the 
medullary rays have more meager contents, and towards the 
stem axis they became larger. That there is a “ xylem sheath” 
characterized by cells of greater size and richer contents such as 
Zenetti describes for O. vegalis, | cannot affirm, and certainly 
there is not such a sheath in QO. Claytoniana. 
PHLOEM.—The tissues that have just been described are 
bordered by the phloem, which consists chiefly of sieve tubes. 
Parenchymatous cells are sometimes met with in isolated posi- 
tions in the metaphloem, and between the metaphloem and the 
Protophloem they constitute a more or less broken layer, most 
Pronounced in O. Claytoniana, and least constant in O. regalis and 
I. barbara.’ The sieve tubes are strongly developed and are of 
the “type vigne” of Lecomte. They are large, have thin walls 
of unmodified cellulose lined with a delicate layer of protoplasm, 
and are devoid of nuclei. They are provided with oblique 
terminal walls and are furnished with sieve plates both simple 
and compound. The sieve plates are covered with ‘‘olobules 
brillants,” and by treatment with proper reagents callus plugs 
may be demonstrated in them. The sieve tubes of the proto- 
Phloem are smaller than those of the metaphloem and their 
terminal walls are not as oblique. 
As there has been considerable difference of opinion regarding 
™ ZENETTI: Das Leitungssystem im Stamm von O. rega/is. Bot. Zeit. 53:63. 
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