of Fossil Plants of the Coal-Measures. 3 1 7 
conditions of common occurrence amongst these objects. 
At a, a, we have some isolated spherical cells. At b , b , are 
similar ones, but of much smaller dimensions. At c is an oval 
cluster of a form that is not uncommon. It looks like a group 
of cells, of various sizes, enclosed either within a mother-cell 
or within some viscid substance that binds the cluster together 
in a defined manner. At d is a somewhat less defined but 
otherwise similar cluster, though of larger size. 
Fig. 3 is another host-cell from the same fragment of bark, 
but in which all the contained cells retain their spherical 
form. 
Fig. 4 is a host-cell from another fragment of bark ; in its 
centre is a single free spherical cell, whilst numerous others 
exhibit a tendency to adhere to the hostal cell-wall. At the 
lower end of the host a cluster of cells cohere, forming a small 
parenchymatous mass. 
Fig. 5 is a host-cell from a transverse section of a stem or 
rhizome of the type of the genus Anachoropteris of Corda, 
but which is giving off a petiolar branch, apparently identical 
with my Rachiopteris insignis 1 . Many of the cells of the 
inner layer of the cortex of the Anachoropteris are in a con- 
dition very similar to those of Fig. 1. Fig. 6 represents one 
of these host-cells, in which we have two clusters of intrusive 
cells, a and b. At c one of the cells of the group b is filled 
with a cluster of daughter-cells. Innumerable figures might 
be drawn from the above section showing various shapes, 
sizes, and grouping of its intrusive cells ; reference will be 
made to the vessels of this specimen later on. 
Figs. 6 , 7, and 8 are three free cells from another parenchy- 
matous fragment, which respectively contain one, two, and four 
free spherical intrusive cells. Fig. 9 is a host-cell from the outer 
bark of a section of Lyginodendron Oldhamianum , isolated 
cells of which contain intrusive cells in very varied conditions 
of size and grouping. These host-cells are few in number 
compared with those of the cortex which are entirely empty. 
1 Memoir x. Phil. Trans. Part ii. 1880, p. 507. 
