Tyloses in Tracheids of Conifers. 20i 
P. palustris (Fig. 4), in which the tyloses are usually completely 
filled with a dark coloured material. Appearances such as this 
need not be confounded with deposits of resin in tracheids, for the 
shape of a tylosis in tangential section is distinctive, having rounded 
ends, while the masses of resin in the tracheids of Dammara are in 
the form of double concave lenses. 
As to the extent of occurrence of tyloses, it may be gathered 
from the preceding paragraphs that there are two regions of the 
plant in which they may be found, (i.) in the heart wood of the root, 
(ii.) in the first year’s growth of the cone axis. It should now be 
added that, so far as my observations go, they are confined to the 
genus Pinus. I have examined the root wood of thirty-two species 
of gymnosperms, belonging to thirteen genera including Pinus, 
Picea, Larix, Pseudotsuga, Abies, Tsuga, Taxodium, Juniperus, 
Thuja, Taxus, Araucaria, Agathis, Ginkgo, also the cone axes of 
twenty-three species belonging to eight genera, namely Pinus, Picea, 
Pseudotsuga, Cedrus, Abies, Tsuga, Araucaria, Agathis. The 
material has come from a great variety of habitats, and in some 
cases the root wood has included wounded specimens. Only a few 
observations on stem wood have been made in connection with this 
study, but the large number of sections of coniferous wood passing 
through my hands in class-work have failed to furnish any instances 
of tyloses in stems of gymnosperms. These results are at variance 
with those of Raatz (l.c.), who states that tyloses occur in Picea 
excelsa , Larix europcea, Abies pectinata, Thuja occidentalism as well as 
Pinus excelsa, P. silvestris and P. strobus. Unfortunately the only 
figures in Raatz’s paper are of species of Pinus. It may at least 
be suggested that deposits of resin which are common in wounded 
root wood may have been mistaken for true tyloses. My obser¬ 
vations indicate that that these growths occur in both sections of 
the genus Pinus, namely P. strobus (in root and cone), P. nionticola 
(root), P. ayacahuite (cone) among the soft pines, and P. palustris 
(in root and cone), P. rigida, P. austriaca, P. contorta, P. resinosa 
(root), P. silvestris (cone) among the hard pines. 
Wounding has so frequently been adduced as the cause of 
tyloses that I have given special attention to this phase of the 
problem. The presence of wounds may be indicated by distortion 
of the tissues, by resin in the tracheids, and in such genera as 
Abies and Sequoia by the production of a ring of resin canals. 
Judged by these criteria some of the specimens examined were 
wounded, while others showed no signs of abrasion. In some 
