HICK AND CAHU : AFFINITIES OF LEPIDODENDROX. 
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dendron when in a ver}^ young condition, but subsequently 
a pith is found in the centre, which WilHamson describes 
as becoming more massive as the shoot becomes older, 
ii. In Lycopodium the cross section of the axile C)dinder 
l)resents the xylem in the form of a number of distinct 
bands. In Lepidodendroii the elements of the xylem 
are not arranged in distinct bands, and for the most 
part are in contact laterally as well as radially. Further, 
the increase in size of the elements, from the periphery 
inwards, is not nearly so regular as in Lycopodium. 
iii. In Lycopodium the phloem not only forms the peripheral 
part of the axile cylinder but is also intercalated between 
the bands of x)dem. In Lepidodendron the phloem 
appears to be entirely outside the xylem. 
iv. LAjcopodium possesses both a phloem sheath and a bundle 
sheath, but these have not yet been found in Lepido- 
dendron. Little importance, however, can be attached 
to this difference until more positive evidence is obtained. 
It is well within the limits of probability that better 
preserved specimens than those yet discovered may 
show the existence of one or more sheathing layers. 
v. The matured cortex of most species of Lycopodium 
frequently shows both hypoderma and inner parenchyma 
more or less sclerenchymatous. This is not the case 
with Lepidodendron selaginoides. Here the inner 
parenchyma is a soft thin-walled parenchyma, rich in 
intercellular spaces, and the innermost layers of cells have 
a radial arrangement. The hypoderma is composed of 
elements whose walls are somewhat thickened, but as the 
mechanical function is soon thrown upon the sclerenchy- 
matous secondary phelloderm, the thickening is limited. 
B. Lepidodendron and Selaginella. 
L Agreements. 
i. In both Selaginella and Lepicbdendron the hypoderma 
generally consists of more or less thick-walled elements, 
in which few or no intercellular spaces are met with. 
