Some Peculiar Tyloses in Cucumis sativus. 209 
vessel, or (ii.) of much larger size and pressed against one another, 
thus becoming polyhedral in shape and forming an apparently 
continuous parenchyma filling up the cavity of the vessel (Fig. 2). 
Nuclei can often be observed in these cells. It is difficult to 
trace a connection between the separate cells of this tissue and the 
parenchymatous cells adjoining the vessel, but Molisch was able, by 
adding dilute chromic acid, partially to disintegrate the wall of the 
vessel and thus find the connection between the two, proving the 
tyloses to have arisen as out-growths from the neighbouring paren¬ 
chymatous cells. 
An exceptional case of tyloses, remarkable in so far that 
although found in an herbaceous stem the outgrowths have 
lignified walls, was found in a specimen of Cucumis sativus. In 
this specimen both forms of thin-walled tyloses already described 
were found to exist, the smaller ones often in the same vessels as 
the thick-walled form. The lignified tyloses remain oval in shape 
and never come together to form a continuous tissue as is so often 
the case with the unlignified tyloses. 
In microtome sections a distinct connection can be traced 
between these thickened tyloses and the cells adjoining the vessel 
(Figs. 4 and 5), from which cells the tyloses have originated. The 
subsequent thickening prevents the tyloses from extending further 
into the vessel and they are never found to obstruct the passage 
completely. The lignified tyloses have pitted walls, the pits being 
either short and oval (Fig. 1, a , c), or long and narrow (Figs. 1. b, 
d , and 4) in which latter case they often approach a spiral arrange¬ 
ment (Fig. 4). The smaller pits are also met. with in many of the 
adjoining cells of the wood parenchyma (Figs. 1, 2, 5), while the 
long narrow pits have only been observed in the tyloses themselves. 
In Fig. 1, a vessel is shown which contains in transverse section 
four thickened tyloses besides several normal ones ; the latter are 
smaller and might eventually become thickened like the others, a 
and c are seen in surface view, while b , and d, have been cut 
through medianly and show their contents,—contracted protoplasm 
and nucleus. This is a hand section and rather too thick to show 
the connection between the tyloses and the cells from which they 
are produced as is constantly observed in microtome sections. 
A substance showing the reactions of “wound gum” is very 
often apparent both surrounding the tyloses and lining the vessel- 
wall. It is insoluble in sulphuric acid and caustic potash, does not 
swell up in water, stains brownish-violet with phloroglucin and 
