3 1 8 Williamson . — Anomalous Cells within Tissues 
This Fig. 9 presents a single cluster of closely adherent cells, 
reminding us of those seen at Fig. 2, c. 
Fig. io is a host-cell from the outer bark of another example 
of Lyginodendron Oldhamianum , in which single host-cells 
are isolated as in Fig. 9. In this specimen, as in some 
others, the intrusive cells are very irregular in size and form, 
whilst the spaces within the host which the cells do not occupy 
are filled with a dark brown carbonaceous substance that has 
somewhat the appearance of having once been in a fluid or 
semi-fluid state. There is evidently some connection between 
the presence of this dark substance and that of the intrusive 
cells, since the former is very rarely found in the cells of the 
cortex in which intrusive cells are not present. The above 
observations apply equally to the bark from which Fig. 9 was 
taken. 
I have thus far limited my descriptions to specimens in 
which the intrusive cells occur in various examples of paren- 
chyma, chiefly cortical. But my cabinets contain several 
examples in which the interiors of scalariform vessels or 
tracheids are occupied by cells. In previous memoirs I have 
described two such cases. The first was in Memoir viii, 
where I dealt with my Rachiopteris corrugated , and the 
second in Memoir x 1 2 . Since these descriptions were pub- 
lished I have met with a third example in which similar cells 
occur in the vessels of the inner or non-exogenous zone etui 
medtdlaire ’ of Brongniart), of a yet undescribed species of 
L epidodendron. 
Fig. 11 represents two of the smaller vessels of the vascular 
bundles of Rachiopteris insignis, as seen in a transverse 
section of that petiole, and Fig. 12 is part of a longitudinal 
section of a larger vessel from the same bundle. Each of 
these figures is enlarged 200 diameters. The contained 
cells fill the entire interior of each of these vessels. 
Fig. 13 is a transverse section of two similar vessels, and 
Fig. 14 a longitudinal one of a single vessel, from the inner 
1 Phil. Trans, vol. 161, Part i. p. 214, PI. 6, Figs. 15, 16. 
2 Phil. Trans. Part ii. 1880, p. 506, PI. 16, Figs. 20, 21. 
