On a ‘ Mixed Pith ’ in an Anomalous Stem of Osmunda 
regalis. 
BY 
D. T. GWYNNE-VAUGHAN, M.A., F.R.S.E., 
Professor of Botany in Queen's University , Belfast. 
With Plate XXI. 
I N a paper published by Dr. R. Kidston and myself in the year 1910 an 
account is given of a fossil plant, Osmundites Kolbei , Seward, which 
deserves particular attention because it is the first member of the Osmunda- 
ceae that has been described with a 4 mixed pith \ 1 That is to say, the 
medulla of this plant is not homogeneous, but contains a number of well- 
defined tracheal elements scattered throughout its tissue. It is, in fact, 
exactly the same as the mixed piths that are present in the steles of several 
of the Zygopterideae (Ankyropteris Grayii , A. corrugata , &c.). The dis- 
covery of the existence of a mixed pith in the Order Osmundaceae attracts 
special interest to an anomalous stem of Osmunda regalis that was met with 
in the course of the advanced class-work at Birkbeck College, London, and 
was kindly placed at my disposal by the Head of the Botanical Department. 
The plant in question was not grown in cultivation, but so far as could be 
ascertained was collected at random in a wild condition from a moist 
situation in Cornwall. 
A number of sections, perhaps a dozen or more, were cut from the 
lower end of the stem by the students of the class, in all of which the anomaly 
probably occurred. A few of these were recovered and came into my 
possession together with the remainder of the stem. Further-sections were 
then taken from the exposed end of the stem, but, unfortunately, after three 
or four had been obtained the anomaly abruptly came to an end. 
In the region of the anomaly the stem was 8 mm. in diameter and the 
stele, which contained a ring of nine separate xylem strands, about 2*5 mm. 
In the stele the xylem, phloem, and porose layers are perfectly normal, but 
the parenchyma of the pith contains a large number of scattered tracheal 
elements (Figs. 1 and 2). In one section there are well over sixty of these 
1 Kidston and Gwynne- Vaughan : On the Fossil Osmundaceae, Pt. IV. Trans. Roy. Soc. Edin., 
vol. xlvii, 1910, p. 455. 
[Annals of Botany, Vol. XXVIII. No. CX. April, 1914.] 
