Saxelby . — The Origin of the Roots in Lycopodium Se/ago. 31 
lignification ; they are lignified nearer the tip of the root, i.e. before the 
metaxylem becomes lignified, and are therefore seen clearly after staining 
with cotton red, &c. Figs. 9 and 10 are sections cut near the tip of the 
roots showing the difference between the metaxylem and protoxylem. 
In vertical sections the protoxylem is seen to consist of narrow spiral 
and annular vessels ; while the metaxylem is composed of wide tracheids, 
either scalariform, or with several rows of pits. The phloem shows oval 
plates with pits, on the walls of the elongate cells which form the sieve- 
tubes. 
Outside the vascular bundle of each root is the endodermis, usually 
dividing into two or three layers of cells, the inner and radial walls of the 
inner cells being thickened. The endodermis of an old root is continuous 
with that of the stem. It is surrounded by a wider ring of lacunar tissue. 
The cells separate at an early stage in the formation of the periblem, leaving 
large lacunae ; it is therefore difficult to obtain sections in which this tissue 
is well preserved. In L. Selago the middle or lacunar cortex of the root is 
continuous with the inner cortex of the stem. 
The outer cortex of the root is of cells with thickened cellulose walls 
(see Fig. 12). Each root lying in the cortex of the stem appears to be sur- 
rounded by a layer of mucilage, formed by the partial decomposition of the 
cortical cells of the stem by the absorptive root-cap. 
The structure of the roots of L. dichotomum is very similar to that of 
the roots of L. Selago. The cells of the outer cortex have even thicker 
walls, and they stain slightly with cotton red, though much less deeply than 
does the xylem in the same sections. 
Summary of Results. 
The conclusions I have arrived at concerning the roots of L. Selago 
may be summed up as follows : — 
1. The roots arise near the apex of the stem, but below the first leaves, 
before the vascular elements of the stem have become differentiated. 
2. The roots are derived from a group of cells of the stem, the derma- 
togen of the root from several cells of the innermost layer of the stem 
periblem, the periblem and plerome of the root from the plerome of the 
stem. 
3. The apex of the root is divided into three meristematic regions. 
The dermatogen divides to form both the root-cap of several layers and the 
epidermis ; whilst the periblem forms a covering of about four layers 
of cells over the central plerome of the root. 
4. All the cells of each layer are capable of division, and growth 
by apical cells does not take place. 
5. The roots arising at the apex of each upright stem pass at first 
