q 
266 _ MR. J. R. VAIZEY ON THE ANATOMY AND 
In the centre of the cortex there is the strand of tissues 
(Pl. XI. fig. 28, c.s.), collectively called by Lorentz (17) the central 
strand. Unfortunately the term central strand has also been 
applied by Lorentz to a similar and analogous structure in the 
stem of the oophyte; but there is great anatomical difference 
between the central strand in the one generation and that in the 
other. With figs. 9 and 10 compare Lorentz (17), Taf. xxv. 
83, a; Lorentz (16), Taf. iv. fig. 1; Unger (25), Taf. ii. 9 (Daw- 
sonia superba), Taf. iii. 31. 
The central strand is surrounded by a single layer of thin- 
walled cells (Pl. IX. fig. 11) similar to the cortical cells, 
except that they are on the average longer than the innermost of 
those cells (Pl. XT. fig. 28). These further resemble the cortical 
cells by containing starch-forming plastids, and so differ from the 
tissues of the central strand. This parenchymatous sheath con- 
stitutes the innermost layer of the cortex (exomeristem *), as will 
be shown below. 
The central strand itself consists of certain tissues, which in 
the seta are characterized by the absence of intercellular spaces ; 
it contains two kinds of tissue. One of these forms a solid axial 
cylinder (Pl. XI. fig. 28, a.c.), called Leptoxylem f; the other a 
hollow cylinder concentric with the former (Pl. XI. fig. 28, o.c.) 
called Leptophloém. : 
The Leptoxylem consists of very thin-walled, much elongated 
prosenehymatous cells, whose cell-walls are, as far as can be made 
out, all that remain in the mature seta (Pl. IX. fig. 11). These 
eells do not eontain any living protoplasm, but only here and 
there remnants of disorganized protoplasm. This conclusion has 
been come to after very careful examination and comparison of 
sections, both transverse and longitudinal, in which nothing more 
than a few granules, the last remains of the protoplasm of the 
meristematic cell, were found. 
The Leptophloém is a more extensive tissue-system than the 
leptoxylem, and it consists of thick-walled, considerably elon- 
gated cells (fig. 28, o.c.), forming in transverse section a zone two, 
rarely three or more, cells deep. The innermost cells of this 
* Cf. note, p.276. . 
t I. e. Schizogenous intercellular spaces; lysigenous spaces sometimes occur 
in some of the Splachnaces ; in Splachnum sphericum, Linn. fiL, there is a 
large lysigenous space in the centre of the leptoxylem. 
1 See for explanation of these terms, p. 275. 
