3 1 6 Bailey . — A Cretaceous Pity oxy Ion with Marginal Tracheides. 
case in living pines. The abrupt transition from small thick-walled summer 
tracheides of one annual ring to the larger thin-walled spring tracheides of 
the succeeding ring is clearly shown at the base of the figure, and the 
more gradual transition from spring to summer tracheides which takes place 
during the year’s growth may be seen in the annual ring in the central 
portion of the photomicrograph. The resin canals, which are occluded by 
numerous tyloses, are surrounded by large masses of thick-walled and 
highly resinous parenchyma cells, a feature which is without parallel among 
living pines, but which greatly resembles the condition found by Jeffrey 
and Chrysler in Pityoxylon scitnatense. 
Fig. 2 shows a resin canal under higher magnification, and illustrates 
more clearly the thick-walled character of the parenchyma cells and their 
dark resinous contents. 
In these photomicrographs it may be noted that the wood rays contain 
the resinous substance, and that cells adjacent to them are frequently filled 
with it. The latter, however, are not wood parenchyma, since they possess 
bordered pits, but are tracheides into which a portion of the resinous contents 
of the adjacent ray parenchyma cells has been poured. That this is the 
case is clearly shown by longitudinal sections, in which the resinous matter 
may be found passing through the ray pits into the neighbouring tracheides. 
This appears to take place by means of tyloses more or less completely 
filled with resinous secretions. Chrysler 1 in his study of the occurrence of 
tyloses in the tracheides of Conifers came to the conclusion that they 
occurred only in Pinus , in the heartwood of the root and in the cone axis. 
Since these regions are often the seat of ancestral or primitive characters, 
the occurrence of tyloses in the stem of a Cretaceous Pityoxylon seems to 
indicate that these structures are ancestral, and occur only in primitive 
regions of modern pines. This conclusion, however, is not entirely sub- 
stantiated by a study of the stem wood of living pines, as I have found 
indications of tyloses in the tracheides of several species. Fig. 5, a transverse 
section, illustrates the occurrence of tyloses in the stem wood of Pinus 
Strobus , L. 
Fig. 3 shows the tangential section of the lignite under a low magnifi- 
cation. The rays are obviously of two kinds, linear and fusiform, which 
are characteristic of Pityoxylon, Kraus. The fusiform rays are seen to 
contain horizontal resin canals, occluded by numerous tyloses. The highly 
resinous character of the ray parenchyma is clearly shown in this section, 
and it may be noted that the walls of the tracheides have been crushed 
together by lateral pressure, whereas the ray parenchyma cells have retained 
their natural form. This condition is probably accounted for by the 
resinous contents of the rays. 
1 Chrysler, M. A. : Tyloses in the tracheides of Conifers. The New Phytologist, vol. vii, 
No. 8. 
