Saxelby. — The Origin of the Roots in Lycopodium Selago. 23 
root is not formed from the pericycle, but from a deeper layer, whilst 
the cortex and cap are alone developed from the pericycle. 1 Van 
Tieghem regards this simply as a case of retarded root formation, and 
differs from Lemaire, amongst other points, in attributing the formation of 
all the tissues of the root in A. odorata to layers within the pericycle. 
The Origin of the Roots. 
The earliest stages of root origin in L . Selago were found by cutting 
transverse and vertical sections through the upper end of the shoots of 
young plants grown from bulbils, at a stage when the stem bore only 
a few leaves (from 3 to 10). The chief difficulty in obtaining the very 
early stages lies in the fact that the roots arise near the apex of the 
stem, below the origin of several leaf-traces, and often on a level with 
others. In this region all the tissues of the stem are in a meristematic 
condition, and the central cylinder is not clearly differentiated from the 
surrounding cortex. The beginnings of the leaf-traces might therefore 
be readily mistaken for those of roots. A little lower down the stem, 
the innermost layers of the cortex are dividing to form the endodermis 
and the so-called pericycle, and possibly Bruchmann, who attributes 
the root origin in L. inundatum to a few cells in these layers, has mis- 
taken these divisions for those of root origin. 
In the earliest stages of what are undoubtedly roots, all the cells 
taking part in root formation are characterized by their large size and 
dense protoplasmic contents, and the region of cells affected includes 
nearly half of the central cylinder of the stem. One of the youngest 
roots of which I obtained a section is shown in Fig. 1, arising from the 
stem, which is here cut transversely. The central plerome of the stem 
is of small cells, none of which are differentiated into xylem or phloem. 
Surrounding this is a ring of cells (i) varying in size and intermediate 
between the small inner cells of the plerome (pi) and the large cells of 
the cortex (c). The innermost row of cortical cells has divided to form 
two or three rows of inner cortex, and in some parts the intermediate cells 
appear continuous with the radial rows of cells formed in this way. The 
intermediate cells therefore I consider are derived from the periblem, and 
probably at a later stage form the characteristic endodermis. The section 
figured is through the centre of the root origin, that is to say, it is the section 
showing the root origin at its widest point. No other sections of the series 
show cells farther out in the inner cortex having the dense protoplasmic 
contents characteristic of the root origin. It is seen from the figure that the 
outermost layer of cells of the root origin is continuous with the intermediate 
layer of cells, which cannot be defined with certainty either as pericycle or 
endodermis, though apparently derived from the periblem. In other 
1 Lemaire, loc. cit., p. 234. 
