Secondary Xylem in P silo turn* 517 
Nageli (’58) : Das Wachsthum des Stammes, Beitr. zur wissensch. Bot., Heft I. 
Nageli und Leitgeb (’68): Entstehung u. Wachsthum der Wurzeln, Beitr. zur wissensch. Bot., 
Heft IV, p. 73. 
Pritzel (’ 00 ) : Psilotaceae in Engler and Prantl, Die natiirl. Pflanzenfam., 1. Teil, Abt. 4, p. 606. 
Russow ( 72 ) : Vergleichende Untersuchungen, Mem. de PAcad. de St.-P^tersbourg, 7® sdr., 
t. xix, no. 1. 
( 75 ) : Betrachtungen iiber das Leitbiindel- und Grundgewebe. 
Scott (’ 00 ) : Studies in Fossil Botany. 
( ’ 97 ): On Cheirostrobus, Phil. Trans., series B, vol. 189, p. 1. 
Solms-Laubach (’ 84 ) : Der Aufbau des Stockes von Psilotum triquetrum , Ann. Jard. Bot. de 
Buitenzorg, iv. 
Thomas (’02) : The affinity of Tmesipteris with the Sphenophyllales, Proc. Roy. Soc., vol. Ixix, 
P- 343 - 
Williamson ( 74 ) : On the organization of the Fossil Plants of the Coal-Measures, Part V, Phil. 
Trans., 1874, p. 41. 
EXPLANATION OF FIGURES IN PLATE XXXIII. 
Illustrating Mr. Boodle’s paper on Psilotum. 
Figs. 1-6 are photographs from sections of Psilotum triquetrum stained with methyl-green and 
eosine ; they are all x 90. 
Fig. 1. Transverse section of rhizome, showing primary structure only. The xylem consists of 
a solid group of nine tracheides (seven quite distinct and two small paler ones on the left). 
e , endodermis ; s. t., sieve-tubes. 
In Figs. 2-6 numerous secondary tracheides are present, many of them being incompletely 
lignified and therefore stained dark. 
Fig. 2. Transverse section of the stem, cut at d in Text-Fig. 44. The large pale-walled primary 
tracheides ( p ) are surrounded by a large number of secondary tracheides. 
Fig. 3. Transverse section of the stem, cut at c in Text-Fig. 44. s, a group of secondary 
tracheides. Primary xylem band-shaped and probably diarch. 
Fig. 4. Transverse section of the stem, cut at a in Text-Fig. 44. Primary xylem band-shaped. 
Fig. 5. Transverse section of the stem cut half-way between a and b in Text-Fig. 44. Primary 
xylem triarch, r, parenchymatous ray opposite one of the protoxylem-groups. 
Fig. 6. Transverse section of the stem, cut at b in Text-Fig. 44. Xylem triarch. Radial 
arrangement of elements shown at r. 
Nn2 
