JOURNAL OF AM1TOAL RESEARCH 
DEPARTMENT OF AGRICULTURE 
Voe. I Washington, D. C m March 25, 1914 No. 6 
TYLOSES: THEIR OCCURRENCE AND PRACTICAL 
SIGNIFICANCE IN SOME AMERICAN WOODS 
By Eloise Gerry, 
Micro scopisi, Forest-Products Laboratory, Forest Service 
GENERAL DESCRIPTION OF TYLOSES 
The large open pores or vessels conspicuous in hardwoods frequently 
become closed by growths called tyloses. 1 These growths render the 
wood practically impermeable to air and liquids. On the split surfaces 
of a wood such as white oak or pignut hickory the tyloses appear in the 
vessel channels as glistening cellular growths resembling masses of soap 
bubbles. (PI. LII, fig. 1.) These masses are protrusions from the living 
parenchyma cells of the wood itself into adjacent vessel or tracheid cavi¬ 
ties. They enter at the thin places or pits in the wall of the wood ele¬ 
ments (see PI. LII, figs. 2 and 3), and expand to a greater or less degree. 
In the softwoods (PI. LVI, fig. 1) tyloses are relatively small, but in the 
hardwoods they frequently form bladderlike sacs of considerable size 
(PI. LII, figs. 2 and 3, and PI. LIII, figs. 1,2, and 3), often developing 
simultaneously in many of the parenchyma cells surrounding the tube¬ 
like vessel cavities. (PI. LII, fig. 3.) Under such circumstances, if 
growth is vigorous, the tylosal sacs, after pushing into the vessel cavity, 
grow together, completely filling it. In this way the ability of the 
vessel to conduct air or liquid is effectually checked. (PI. LIII, figs. 1 
and 2.) Sometimes, however, the tylosal growths do not entirely fill the 
vessel, and only a clogging action results. 
The purpose of this study was to determine the occurrence of tyloses in 
the most important commercial species of native woods and their signifi¬ 
cance in relation to the adaptability of these woods to certain practical uses. 
Observations were made not only of the presence or absence of tyloses 
in a species, but also of the extent and degree of development and the 
regions (sapwood or heartwood) where the growths are found. 
1 The$e growths received, in 184s, the name “ThyUe” (tyloses) from a German botanist who signed as 
“Ungenannte,” or ''unknown,” the paper discussing them. This writer is, however, believed by Boehm 
and Winkler to have been Frl. Hermine von Reichenbach. The name " Thylle ” is derived from the Greek 
word 6 Mcc, meaning a purse or sack. The occurrence of tyloses was, however, noted as early as 1675 by 
Malphigi, in the drawing of a cross section of chestnut wood. They are also given the descriptive name 
"Fiillzellen,” or filling cells, by the Germans. 
(44s) 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
Vol. I, No. 6 
Mar. 25, 1914 
