82 
F. E. Weiss. 
ON THE TYLOSES OF RACHIOPTERIS CORRUGATA, 
By F. E. Weiss, D.Sc. 
[With Text Figs. 12 and 13]. 
N his description of this fern-stem, Williamson 1 (’77) drew 
attention to the presence in its tracheids of “ densely packed 
masses of cells,” which he compared with the tyloses found in the 
vessels of recent plants. A similar occurrence was noticed by him 
in a fern rachis described under the name of Rachiopteris insignis 
(’80). Recently Oliver 3 (’05) has found these petioles associated 
in such a way with the stem of Rachiopteris corrugata as to suggest 
that these two remains are the stem and leaf-stalk of the same plant. 
A similar section is in the collection of the Manchester Museum, 
being one of the specimens belonging to the late Thomas Hick. 
The occurrence of tyloses in both organs might be looked upon as 
confirmatory evidence of the connection of two fern-remains. 
The identification of the remarkable “intrusive cells” with the 
tyloses of recent plants was again urged by Williamson 3 (’88) in a 
publication in which he discussed several cases of anomalous cell- 
contents in fossil plants. It was, of course, quite possible to consider 
these intrusive cells to be of the nature of saprophytic or parasitic 
fungi, as they undoubtedly are in some of the cases described by 
Williamson. But in the two fern-remains mentioned the general 
appearance of the blocked-up tracheids is so remarkably like that 
of vessels filled with tyloses, that one is inclined to accept 
Williamson’s conclusions in spite of the fact that such tyloses have 
not been found in any living ferns according to Molisch 1 (’88), who 
made a most careful examination of about 700 plants with a view 
to ascertaining the distribution of these curious cells. Nor is it 
surprising that they should be absent from Ferns and Gymnosperms, 
when we consider that their main function is probably to close 
continuous vessels. For these latter are generally absent from the 
two groups of plants referred to, which, possessing tracheids, have 
1 Williamson, W. C. Organisation of the Fossil Plants of the 
Coal Measures, Part VIII., Phil. Trans., 1877. Part X., 
Phil. Trans., 1880. 
3 Oliver, F. W. Catalogue of the Collection of Sections of Fossil 
Plants in the Botany Department of University College, 
London, 1905. 
3 Williamson, W. C. On some anomalous cells developed within 
the interior of the vascular and cellular tissues of Fossil 
Plants of the Coal Measures, Annals of Bot., Vol. II., 1888. 
4 Molisch, Hans. Zur Kenntniss der Thyllen. Sitzber. d. k. 
Akademie d. Wiss. zu Wien., Bd. XC., VII., 1888. 
