On the Tyloses of Racniopteris corrugata. 85 
and-a-half years ago in this Journal. 1 As will he seen from the 
accompanying sketches (Figs. 12 and 13), in this particular instance 
the cellular protrusion differs from the ordinary tyloses in having 
its walls thickened (probably lignified), and the thickening has taken 
place in such a manner as to give the structure the appearance of 
a small pitted tracheid. As the pits are of irregular shape and 
somewhat pointed, the marking at first sight looks slightly spiral. 
This is exactly the appearance of those described by Miss Jordan, 
and there is thus a very close agreement between this thickened 
tylose of Racliiopteris corrugata and those from a section of Cucuniis 
figured in Plate X. of Vol. II. of the New Phytologist. These 
latter are undoubted tyloses, as their protoplasmic contents and 
nuclei were often visible. It was noticeable in the case of these 
latter that they only occurred in vessels which were not yet blocked 
by ordinary tyloses, while as the one figured in this note shows, the 
peculiar tylose in Racliiopteris occurs in a vessel in which the lumen 
is occluded by thin-walled cellular tissue, as it is in the adjoining 
vessels. It is, of course, possible that it may have been formed 
earlier than the thin-walled tyloses, and indeed its more or less 
spherical shape suggests that it had become thickened before it had 
met the outgrowths from the other sides of the vessel. In Cucuniis, 
too, it is quite conceivable that vessels in which the lignified tyloses 
were formed might subsequently become closed by the ordinary form 
of outgrowths, for numerous young thin-walled tyloses were met with 
and are figured by Miss Jordan among the thickened ones. There 
seems therefore in this particular to be no real difference between 
the anomalous tyloses met with in two such widely different plants 
as a fern of the Coal Measures and a dicotyledon of to-day. The 
occurrence of this anomalous tylose of course greatly strengthens 
the probability of the thin-wall protrusions being also of the nature 
of tyloses. At the same time we still remain unable to explain satis¬ 
factorily the mode of origin of these intrusive cells, for the anomalous 
tylose also arises in a tracheid apparently surrounded on all sides 
by lignified cells. It will, however, be seen that it, like most of the 
thin-walled protrusions, arises near the angle formed by adjoining 
tracheids, and thus points to the possibility of the existence of 
hidden parenchymatous cells in these angles. 
In conclusion I should like to mention that we have in the 
collection of the Manchester Museum a section of Zygopteris 
Gray 'd (R443) which has a few tyloses both in tracheids of the stem 
and also in one of the leaf-trace bundles. 
1 Jordan, Rose. On some peculiar tyloses in Cucuniis sativns, 
New Phytologist, Vol. II., No. 9, November, 1903. 
