Saxelby . — The Origin of the Roots in Lycopodhim Selago. 25 
which divides tangentially to produce the periblem of the root, which usually 
consists, even in the young root, of two or three layers of cells at the apex 
(Figs. 1 and 2). It cannot be said with certainty which layer of undifferen- 
tiated tissue of the stem first produces this meristem, but it is certainly 
produced from a portion of the plerome. The plerome of the root is also 
directly derived from that of the stem, but the root arises at a stage when 
the vascular elements of the stem are undifferentiated. In Fig. 4 the 
xylem masses of the stem are seen not yet united in the centre of the stele, 
and all the xylem cells are not yet lignified. The centre of the root base 
is seen to be connected with the phloem, though the two xylem groups of 
the stem, one on either side of the root base, have not yet become 
connected with the root xylem. All the tissues of the root are still in 
a meristematic condition, but the apex, showing the three distinct meri- 
stematic regions, is found several sections (about 250 \x) lower down the 
stem, lying completely in the stem cortex. 
Bruchmann 1 states that the tracheids in L. inundatum only appear at 
the base of the root when the latter breaks through to the outside, but in 
L. Selago , owing to the longer period which the root passes in the stem 
cortex, the xylem is differentiated before this point is reached. Jones 2 (in 
describing L. Selago ) as well as Bruchmann 3 (referring to L. clavatum and 
L. inundatum) agree that the phloem of the root is directly connected with 
that of the stem, and Van Tieghem 4 states that the root of Z. inundatum is 
formed in the pericycle opposite the place where a phloem bundle will 
form later. 
The above conclusions are drawn from a study of transverse sections 
of stems at varying ages. Vertical sections near the apex of the stem show 
these points less clearly, since such different conclusions may be drawn 
from sections which are slightly oblique or not exactly median, and also 
since the stem endodermis does not stain except where the roots have begun 
to dissolve the surrounding tissues. 
Fig. 5 represents a vertical section of a young shoot grown from the 
bulbil, and shows a young root origin. The dermatogen of the root, of one 
layer of cells, appears continuous with the innermost layer of wide cortical 
cells. The periblem and plerome of the root are continuous with several 
rows of cells of the stem plerome. The enlarged cells forming the base of 
the root plerome are seen to come into contact with one of the annular 
vessels of the stem, but no vessels are formed as yet in the root itself. The 
plerome cells of the stem are distinguished by their narrow elongate form, 
and elongate darkly-staining nuclei ; in some sections round or oval sieve- 
1 Bruchmann (£), loc. cit., p. 81. 
2 Jones, Morphology and anatomy of the stem of Lycopodium. Trans, of Linn. Society, 
2nd ser., Botany, vol. vii, Pt. II, 1905, p. 29. 
3 Bruchmann ( 6 ), loc. cit., p. 79 & c. ; Fig. 31, Taf. iv. 
4 Van Tieghem, loc. cit., p. 556. 
