1907-8.] Morphology of the Cone of Lycopodium cernuum. 359 
middle of this face that dehiscence takes place. The point of dehiscence is 
immediately opposite the small space between the sporophylls, and is marked 
by an x in the lowest sporangium on the left-hand side of fig. 1. 
The disappearance of the mucilaginous mass from the sporophyll-base 
explains the strongly peltate form of the sporophyll in Pritzel’s figure.* 
To this extent the sporophyll might better be termed pseudo-peltate. In 
L. cernuum the sporophyll is also truly peltate though only slightly so. In 
the radial section (fig. 1) a small downgrowth of the outer margin of the 
sporophyll-base ( m.a .) can be seen lying against the surface of the sporangium 
immediately below. In a young stage of development this marginal growth 
fitted in between the sporangium and its sporophyll, but has become removed 
from this position, which originally determined its form, by the further 
growth of the cone. The marginal appendage, unlike the persistent tissue 
above, is bounded on both sides by an epidermis, with usually a single layer 
of mesophyll ; its cells are throughout thin- walled. The sporangium at its 
origin is situated close to the axis of the cone, and its distal position when 
mature is due to subsequent growth of the basal region of the sporophyll ; 
this takes place after the mucilage cavity has been formed. 
The structure described above is characteristic of all the sporophylls of 
any mature cone except those at the base and those at the summit. In the 
basal sporophylls the mucilaginous change does not extend to the surface of 
the sporophyll-base and the mucilage cavity is bounded by one or more layers 
of cells. In this respect, though not in their general form, these sporophylls 
are intermediate between the sporophylls above and the vegetative leaves. 
Towards the apex of the cone the sporophyll-bases are inserted at an 
increasingly acute angle, and on the upper sporophylls arrested sporangia 
are constantly found. In these abortive sporangia the stalk is normally 
or even excessively developed, while the small cavity is occupied by a 
degenerated mass of spore-mother-cells. The sporophylls in this region, 
being arrested in earlier stages of their development, often have the mucilage 
cavity still limited by a layer of cells. 
A consideration of the relative positions of the parts in the sporophylls 
of the alternating whorls on the opposite sides of the axis in fig. 1 will 
make it clear that the leaf -bases of any one whorl (a) must hang down 
between the sporangia of the alternating whorl below ( b ) and reach to the 
level of the sporophylls of this whorl. What the radial section does not 
by itself demonstrate is the fact that the sporophyll-base is coherent with 
the margins of the two sporophylls between which it lies. This is seen in 
the tangential section of the cone (fig. 2). If the outline of any one leaf- 
* Loc. cit ., fig. 379, E. 
