Jeffrey. — On the Structure of the Leaf in Cretaceous Pines. 215 
In the case of Figs. 18 and 19 it is, however, by no means certain that there 
is no parenchyma intermingled with the outer transfusion elements, although 
the tracheidal cells are in any case infinitely more abundant than they are 
in living Pines. In the two species under discussion the endodermis is not 
clearly marked and may well be absent. The mesophyll is very scanty in 
amount, and lacks the infolded walls which characterize it in living species 
of Finns. 
Fig. 20, PL XIV, shows a somewhat smaller leaf of a Cretaceous Pine 
than those shown in the two previous figures, but its organization is of the 
same general type. The state of preservation is more favourable to the 
differentiation of the inner transfusion sheath than in the foregoing species. 
It may also be somewhat clearly distinguished, although the magnification 
is low, that the xylem of the bundle is entirely centrifugal, a condition which 
we have found to be present in all true Pines from the Middle Cretaceous of 
Staten Island. Fig. 21, PI. XIV, shows a highly magnified longitudinal sec- 
tion of the bundle in this species. The inner transfusional sheath appears as 
very thick- walled, dark-coloured cells, which in the vicinity of the protoxylem 
are very considerably elongated and possess a very narrow lumen. Passing 
towards the left in the figure, the transfusion elements become at first more 
nearly isodiametric and then much thinner-walled. On the extreme left 
they have suffered disorganization. On the side of the xylem near the 
inner transfusional sheath are to be made out the somewhat disorganized 
ringed and spiral elements of the protoxylem. There is no indication 
whatever of the presence of true centripetal elements, such as are to be 
found in the foliar bundles of Prepinus as described above. Further to the 
right the centrifugal elements become reticulated and finally pitted, although 
the latter condition is not clearly shown in the figure. 
Fig. 23, PL XIV, shows the cross-section of another leaf of Pinus 
belonging to still another Cretaceous species, which, we may judge from the 
angle made by its two plane surfaces, came from a five-leaved fascicle. In 
this case the inner sheath of the transfusion tissue has become almost 
obsolete and appears most clearly on the side of the vanished phloem and 
between the bundles. Fig. 22 reproduces the transverse section of another 
leaf, which probably belonged to a three-leaved fascicle. The inner trans- 
fusional sheath in this case can be distinguished rather better on the side of 
the phloem than in the last described species. It has suffered disintegration 
between the bundles, but again appears at the back of the protoxylem. 
Fig. 24 shows the transverse view of a very large leaf which has become 
considerably flattened in process of fossilization. The inner transfusional 
sheath can be clearly distinguished except on the flanks of the bundles, 
where in all species it tends to be thin. 
It is obvious from the data supplied in the foregoing paragraphs that 
the leaves of species of true Pines from the Middle Cretaceous of Staten 
