Saxelby . — The Origin of the Roots in Lycopodium Selago. 29 
obliquely downwards. It becomes surrounded with its own cortex, and 
reaching the base of the bulbil, it passes to the outside, curving round until 
appearing to come from the centre of the base. The stem bundle persists 
as a simple structure like a leaf-trace, passing actually through the lower 
epidermis of the bulbil, and broken short at the point where the bulbil 
separated from the stem. This first root bundle lies between the concave 
surface of the bulbil and the stem stele (see Fig. 8). Cramer 1 showed that 
the first root arose while the bulbil was still attached to the parent plant ; 
but he said it arose at the point of separation of the bulbil. A vertical 
section, in the plane passing from concave to convex side of a bulbil taken 
from the stem, shows the first root with the meristematic apex still in the 
cortex of the bulbil shoot. Such sections through the largest bulbils found 
on the stem show at the same time a second root close to the apex of the 
stem of the bulbil, on the same side of the stele as the first root, but below 
two or three leaf-traces. Bruchmann 2 worked at the young sporophytes 
of L. Selago grown from prothallia, and found that the first root was con- 
tinuous with the central vascular strand of the stem. 
The Structure of the Roots. 
As I have already stated, the old root is continuous at its base with 
two protoxylem groups of the stem and the intervening phloem. Bruch- 
mann 3 and Jones 4 both found this to be the case in the species they 
examined, and Bruchmann and Van Tieghem 5 agree in saying that the 
roots arise opposite the phloem groups. Working at L. Selago I noticed 
sections of one specimen in which the root was connected with three proto- 
xylem groups ; and Miss Wigglesworth 6 figures a similar case for the first 
root of L. complanatum . In no section of L. Selago was a root seen to be 
connected with only one xylem group. The leaf-traces, on the contrary, 
never connect with more than one group of protoxylem cells. This difference 
between the root and leaf-traces is noticeable in all stems in which the 
xylem and phloem are differentiated. In the region of origin of the roots, 
however, the cells of the stem plerome all appear alike ; but even here the 
leaf-trace origin and root origin can easily be distinguished by the amount 
of stem plerome affected in each case. During root origin half the plerome 
or more consists of enlarged cells with dense protoplasmic contents and 
large, darkly-staining nuclei, whilst only a few cells of the plerome are 
differentiated for the origin of a leaf-trace, and even these are not especially 
1 Cramer, Pflanzenphys. Untersuch. v. C. Nageli u. C. Cramer, 1855, v °h iii> P- l 9- 
2 Bruchmann (6), loc. cit., p. 101 ; also Fig. 42 u. 43, Taf. vii. 
8 Bruchmann (b), loc. cit., p. 81. 4 Jones, loc. cit., p. 28. 
5 Van Tieghem, loc. cit., p. 556. 
6 Wigglesworth, Young Sporophytes of L. complanatum and Z. clavatum. Annals of Botany, 
vol. xxi, No. lxxxii, April, 1907, Fig. 1, p. 224. 
