32 Saxelby . — The Origin of the Roots in Lycopodium Selago. 
obliquely, then directly down through the middle cortex. They only 
appear at the outside beneath the soil and on the under side of the obliquely 
growing stem. 
6. Normally the roots are arranged in the cortex on all sides of the 
stele, but where the stem has grown obliquely to the ground plane all 
the roots are found in one half of the cortex of the stem. 
7. The roots of this species do not dichotomize before leaving the 
cortex of the stem. 
8. The bulbil, while still on the stem, may show the origin of two roots. 
The first-formed root curves round in the cortex, and, after separation of the 
bulbil from the stem, occupies a central position at the base of the green 
shoot. 
9. Each root is connected with two protoxylem groups of the stem 
and the enclosed phloem. Exceptionally one may be in connexion with 
three groups of protoxylem, but never with only one. Leaf-traces, on the 
contrary, are never connected with more than one set of protoxylem 
elements. 
10. The roots may be diarch or tetrarch, the metaxylem being arranged 
in two parallel bands in the former case, and in the shape of a horse-shoe in 
the latter. The protoxylem may occur all round the outer edge of the 
metaxylem, leading to the production of types intermediate between 
tetrarch and diarch. A diarch root may become tetrarch, or vice versa. 
11. The protoxylem is formed of spiral and annular vessels; the 
metaxylem is of wide tracheids, either scalariform or with several rows 
of pits. The endodermis is of two or three layers, the cells of the innermost 
layer having thickened radial and transverse walls. The middle cortex 
shows large lacunae, which, however, do not communicate with those of the 
middle cortex of the stem. The roots are provided with a firm outer 
cortex of thick-walled cells, surrounded by the mucilaginous remains of the 
cells of the stem which have been decomposed by the root-cap in the 
downward growth of the root. 
In conclusion, I wish to acknowledge my indebtedness to Prof. F. E. 
Weiss for his kindness in advising me with regard to this piece of work, and 
for the helpful criticism he has given. 
