22 MR. C. E. JONES ON THE MORPHOLOGY 
group of three plants with L. tnundatum, Drummondii, and alopecuroides, all of which 
grow in swampy ground; it would be interesting to know whether they all have 
mucilage-cavities. In the course of the present investigation no other species was found 
which contained mucilage-cavities normally. This species furnishes an instance of a 
plant provided with xerophytic modification which nevertheless grows in water-logged 
soil. This may be ascribed to the fact that it grows in soil which is rich in humus, and 
that these modifications are necessary for the plant to obtain and keep the necessary 
water. Generally the stem keeps close to the ground, produces a considerable number 
of roots, branches freely when it is growing quickly, and the apices are markedly 
orthotropic. The strobilus is produced in drier situations, and the structure of this part 
of the stem is radial. 
The best-grown specimens show eight to ten protoxylems (Pl. 4, fig. 19), but frequently 
they are fewer and in the branches a striking tetrarch structure is obtained (fig. 20). 
Hegelmaier gives a small figure of the same type as that shown (fig. 27), but his figure 
does not indicate the protoxylems, which are clearly distinguishable from the metaxylem. 
The amount of xylem is very considerable compared with the phloem, as there is a 
central plate of xylem ; and, further, the xylem is very broad at the periphery, where it is 
in juxtaposition to the pericycle, whereas the phloem is partieularly narrow. This 
tetrarch structure is regarded as a reduced condition. 
The cells of the cortex are nearly all thin-walled, but there is an appreciable amount 
of variation in the centrally situated cells in plants taken from different localities. In 
some, air-spaces are well marked, but in others, where the cells are more compact, the 
mucilage-cavities are better developed. The mucilage-cavities lie outside the leaf-trace 
bundle, and run some distance upwards into the leaf and pass down into the stem, but 
stop at the base of the leaf in the strobilus. 
LxcoPopivM SELAGO, Linn. ; LYCOPODIUM SERRATUM, Thunb. 
Both of these species are included in Mr. Baker’s first group, of which L. Selago is 
taken as the type. The erect growth of L. Selago is well known, but Z. serratum is sub- 
erect and may grow much longer than the former ; otherwise there are several noticeable 
points of similarity—e. g., in the indefinite arrangement of the sporangia, the unequal 
development of sporophylls, the formation of bulbils, and the manner in which the roots 
grow downwards through the cortex of the stem. The vascular cylinder in ZL. Selago 
is small (Pl. 4. fig. 21), the number of protoxylems is at the most six or seven, the xylem 
is flattened out, and, as is generally the case where the protoxylems are few, there is à 
central xylem-portion, so that opposite phioems are not joined. The middle portion of 
the cortex consists of large loosely arranged cells, surrounded by a zone of cells with 
thicker walls. The leaf-bases contain large cavities, as in Z. annotinum. A striking 
feature in sections is the presence of roots, of which as many as seven may be found near 
the base, and these are found to arise quite high up in the plant, even above the point 
where the stem has branched. 
If the stem is growing quite erect the roots do not pass out, but gradually die out, and 
it is only when the stem is growing obliquely that the roots emerge, and thus at the base 
