322 Williamson . — Anomalous Cells within Tissues 
growths from the macrospores of living Selaginelleae affords a 
strong argument against such a conclusion. When I showed my 
specimens to my friend, Hermann Graf zu Solms-Laubach, of 
Gottingen, he at once concluded that the intrusive cells were 
either parasitic or saprophytic. On a later day I also showed 
them to Professor de Bary, of Strassburg, but, whilst recognis- 
ing their existence as an indisputable morphological fact, he, 
with his wonted philosophic caution, hesitated to pronounce 
any opinion as to their nature. Under these circumstances 
it would be presumptuous for me to pronounce dogmatically 
when so high an authority shrinks from doing so. Neverthe- 
less the facts appear to be sufficiently interesting to be put on 
record, hoping that research may some day throw a more 
definite light on the explanation of them. 
The Owens College Botanical Laboratory, 
January 9, 1888. 
EXPLANATION OF FIGURES IN PLATE XVIII. 
Illustrating Professor Williamson’s paper on some Anomalous Cells developed 
within the tissues of the Fossil Plants of the Coal-Measures. 
Note. The cabinet number appended to each description is that of the specimen 
in my collection from which the figure was taken. W. C. W. 
Fig. 1. Fragment of parenchymatous bark, most of the cells of which contain 
intrusive cells, x 124. Cabinet number, 1638. 
Fig. 2. A single cell from the same specimen as Fig. 1. x 262. Cabinet 
number, 1638. 
Fig. 3. Another cell from the specimen Fig. 1. x 262. Cabinet number, 1638. 
Fig. 4. A single cell from another bark-fragment. x 400. Cabinet num- 
ber, 1639. 
Fig. 5. A cell from the bark of a transverse section of a stem of Rachiopteris 
corrugata , Will, x 400. Cabinet number, 264. 
Figs. 6-8. Three cells from a parenchymatous fragment. x 400. Cabinet 
number, 1642. 
Fig. 9. Single cell from the outer bark of a transverse section of a stem of 
Lyginodendron Oldhamianum. x 400. Cabinet number, 1640. 
Fig. 10. Single cell from a tangential section of the outer bark of another 
specimen of Lyginodendron Oldhamiamim. x 400. Cabinet number, 1146. 
