Tyloses in Tracheids of Conifers. 199 
strobus has led me to reinvestigate the subject, for the root in 
question bore no evidence of wounding. I have studied the root- 
wood of as many gymnosperms as were available, and have extended 
the observations to other parts such as wounded branches, the cone 
axis and the short shoots. For valuable aid in securing material I 
am indebted to the following : Mr. C. G. Fraser, Professor T. C. 
Frye, Mr. Andrew Jeffrey, Professor G. R. Lyman, Mr. J. Murdoch, 
Mr. R. Thomson, the Government of British [Columbia, and 
especially to Professor G. L. Goodale and Mr. R. Cameron of the 
Harvard Botanic Garden. 
The typical appearance of the structures in question is shown 
in a tangential section through the heart wood of the root of Pinus 
austriaca (PI. V., Fig. 1). The section was stained in Haidenhain’s 
hematoxylin followed by safranin, and this fact accounts for the 
dark colour of the tyloses, which is due not so much to the cell 
contents as to the nature of the wall, as will be explained later. 
The general form of the tylosis is that of a more or less elongated 
vesicle protruding from a pit in the wall of a central cell of a 
medullary ray into an adjoining tracheid. The appearance is in 
fact precisely similar to what may be observed in the narrower 
vessels in a wood such as hickory; in both cases the tylosis fills the 
whole width of the vessel or tracheid on account of their small 
diameter. The origin of the tylosis is clearly shown in at least one 
case in this figure, and appears even more clearly in certain of the 
other figures. From one of the “ Eiporen ” of a central medullary 
ray cell the thin membrane protrudes, extending farther and farther 
into the lumen of a tracheid. Naturally the marginal cells of the 
rays do not give rise to tyloses, for they have lost their protoplasmic 
contents and have assumed the office of tracheids. A number of 
marginal cells destitute of tyloses may be seen in the various figures. 
A marginal cell may however contain a tylosis, which has entered 
through a pit on the wall between a marginal and a central cell; 
apparently this is not of frequent occurrence. Early stages in the 
formation of tyloses may be seen in Fig. 2, which is a more magnified 
photograph of a section similar to that represented in Fig. 1, viz., 
from the heart wood of the root of Pinus austriaca. Near the upper 
end of the ray is a cell in which the membrane of a pit on each side 
of the cell is inflated, and just below this is a slightly older tylosis. 
The protoplasmic membrane of several of the other cells have 
shrunken, but it will be noticed that the lowest cell (a marginal 
cell) is unaffected. Appearances similar to this but less pronounced 
