204 
Tyloses in Tracheids of Conifers. 
walls ot the vessels are very small—from one-third to one-half the 
diameter of the Eiporen of Pinus strobus, and moreover provided 
with a narrow slit-like mouth-—yet tyloses are so abundant that 
they completely fill the cavity of these vessels. The obscurity of 
the causes leading to the production of tyloses is shown by the fact 
that they are plentiful in Quercus alba, but scarce or absent in Q. 
rubra, although the size of the pits is practically the same in the 
two species. 
Expressed briefly, this investigation goes to show that tyloses 
occur in the heart wood of the root and in the cone axis of members 
of the genus Pinus. In these places tyloses appear to be of normal 
occurrence, but their formation may be induced by wounding. It 
is suggested that these facts may provide an additional reason for 
considering Pinus to be an ancient genus. 
Closely akin to tyloses are the proliferations from cells of the 
“ Luckenparenchym” (Russow 1 ) into the cavities left by dis¬ 
integration of the protoxylem elements. These have been reported 
by various authors as occurring in a number of ferns belonging to 
diverse families. 2 I have confirmed the presence of these growths 
in the stem of Pteris aquilina. They cannot be regarded as true 
tyloses, for they do not occupy the lumen of a vessel or tracheid, 
but are evidently similar in nature. Their occurrence is of interest 
in view of the reporting by Williamson and by Weiss of tyloses in 
the tracheids of fossil ferns. 
1 Russow, Vergl. Untersuch. d. Leitbiindel Krypt. Mem. de 1’ 
Acad. Imp. de St. P^tersbourg 7 ; 19: 80. 1871. 
2 See especially Prantl, Unters. z. Morph, d. Gefasskryptogamen. 
II. Schizaeaceen. Leipzig, 1881. Gwynne-Vaughan, D. T. 
Observations on the Anatomy of Solenostelic Ferns, I. 
Loxsoma. Ann. Botany, 14 : 87, 1901. Boodle, L. A. 
Comparative Anatomy of the Hymenophyllacese, Schizaeaceae 
and Gleicheniaceae, II., Ann. Botany 14: 394, 1901. 
EXPLANATION OF PLATE V. 
Fig. 1. Pinus austriaca. Tangential section through heart wood of the root. 
Tyloses are seen in connection with three medullary rays, x 100. 
Fig. 2. Same. One medullary ray with the initial stages of tyloses. x 200. 
Fig. 3. Pinus strobus. Transverse section through heart wood of root. Pro¬ 
liferations from medullary ray cells into adjoining tracheids. x 160. 
Fig. 4. Pinus palustris. Transverse section through cone axis. Tyloses are 
filled with a black substance, x 100. 
Fig. 5. Same. Tangential section through heart wood of root. Empty 
tyloses and their connection with medullary ray cells. x 45. 
F'ig. 6. Pinus ayacahuite. Tangential section through cone axis. Several 
tyloses, one of which has passed through a pit from one tracheid 
to another. x 125. 
