270 Hill . — (9/z the Presence of a Parichnos in Recent Plants . 
sporophylls. Thus it has been found that the following plants have more 
or less extensive mucilage-cavities in the strobili, but not in the ordinary 
vegetative parts : — Z. alpinum , Z. annotinum , Z. caroliniatum and Z. 
clavatnm. On the other hand these passages have not been seen in any 
part, vegetative or reproductive, of Z. Phlegmaria , Z. squarrosum , and 
Z. complanatum. Z. cernuum has the structure particularly well marked 
both in the cone and vegetative regions (Figs. 12 and 13). 
Taking for an example Z. clavatum , it has been found that the 
development follows an essentially similar course to that already described 
for /. Hystrix, hence no detailed description is requisite. 
A series of transverse sections through a young sporophyll (Figs. 5, 6, 
7 and 8) demonstrate, that in the more distal regions the young 
parichnos consists of two rather ill-defined strands, which in passing 
towards the axis rapidly merge one into the other, so that when the stem 
is reached a broad zone of disorganizing tissue is produced. The examina- 
tion of longitudinal sections shows that this lysigenous degeneration 
extends from the sporophyll into the cortical region of the stem down- 
wards, almost as far as the insertion of the next leaf (Figs. 9, 10 and 11). 
When the canal is fully formed, the parichnos forms a single continuous 
structure, and it shows no signs of bifurcation ; indeed, it is only in the 
youngest stages of development that a double origin can be made out, and 
then only at its distal limits in the sporophyll. Thus a difference is 
exhibited between this plant and Isoetes , but it is to be borne in mind that 
the same dissimilarity occurs in different fossil plants ; for example, Lepido - 
strobus has a parichnos consisting of a single cavity, while Lepidocarpon 
possesses the more usual double arrangement. 
A certain amount of variation is to be found in the strobili of different 
species of Lycopodium , more especially as regards the extent of the tissue- 
alteration. This, however, is a minor point of no consequence, and seemingly 
depends on the shape and other morphological features of the sporophylls. 
The vegetative leaf of Z. cernuum has a prominent canal, and contrary 
to what obtains in the sporophyll, where the cavity never, in any of the 
species examined, extends much beyond the region of the sporangium, it 
traverses the greater part of the leaf, and comes to an end in the cortex of 
the axis. 
Owing to the lack of suitable material, the development of the 
parichnos of the vegetative regions has not been worked out : there is, 
however, no reason to suppose that it follows a course in its formation 
other than the normal. 
As regards other genera of the Lycopodineae, many species of 
Selaginella have been examined, but in no case has anything approaching 
a parichnos been detected, nor has any reference to the existence of mucilage- 
ducts been found in the literature dealing with the structure of this genus. 
