198 M. A. Chrysler. 
TYLOSES IN TRACHEIDS OP CONIFERS. 1 
By M. A. Chrysler. 
Associate-Professor of Botany in the University of Maine. 
[With Plate V.] 
T YLOSES have generally been considered to be absent from 
the wood of gymnosperms. Molisch 2 examined seven hundred 
species of vascular plants in order to determine the distribution of 
these peculiar growths, and came to the conclusion that they are 
altogether lacking in vascular cryptogams and gymnosperms. But 
he was shortly followed by Raatz, 3 who described tyloses occurring 
as the result of wounding in the stem and root wood of Pinus and 
several other genera. Raatz’s paper has apparently been over¬ 
looked, for in so recent a paper as that by Weiss 4 is the following 
statement, “ Their mode of origin, too, upon which Molisch insists, 
as ingrowths from surrounding parenchymatous cells, seems to 
preclude their formation in gymnosperms where wood parenchyma 
is generally absent.” Concerning this statement it should be 
pointed out that absence of wood parenchyma by no means 
precludes the formation of tyloses, for as Raatz figures, and the 
following account shows, tyloses in coniferous wood arise from the 
parenchymatous cells of the medullary rays. Up to the present 
our knowledge of the distribution of these structures may accor¬ 
dingly be summed up thus : tyloses occur in a large number of 
angiosperms as intrusions into vessels, and in gymnosperms (1) in 
the resin canals of a few genera, especially Pinus, and (2) in the 
tracheids of a few genera but exclusively as the result of wounding. 
To this should be added the observations of Conwentz that tyloses 
occupy the cavity of vessels in Cyathea, and that of Williamson* 
and of Weiss (l.c.) who find them in the fossil fern Rachiopteris. 
The observation of certain protrusions from the medullary ray 
cells into the tracheids in the heart wood of the root of Pinus 
1 Contributions from the Phanerogamic Laboratories of Harvard 
University, No. 12. 
2 Molisch, H. Zur Kentniss der Thyllen. Sitzungsber. d. K. 
Akad. d. Wiss. zu Wien 97 ; 7 ; 1888. 
3 Raatz, Wm. Ueber Thyllenbildung in den Tracheiden der 
Coniferenholzer. Berichte d. deutschen Bot. Ges. X., pp. 
183-191. pi. 10. 1892. 
4 Weiss, F. E. On the Tyloses of Rachiopteiis corrugata. New 
Phyt., V., pp. 82—85. 1906. 
6 Williamson, W. C. Organisation of the Fossil Plants of the 
Coal Measures. Part VIII. Phil. Trans., 1877, Part X. 
Phil. Trans., 1880. 
