Mar. 25,1914 
Tyloses in American Woods 
461 
TablH III .—Occurrence of true tyloses in native conifers —Continued. 
Other Conifers —Continued. 
Species. 
Number 
of speci¬ 
mens. 
Sapwood. 
Heartwood. 
Western juniper ( Juniperus occidentalis) . 
1 
None. 
None. 
Red cedar (Juniperus virginiana) . 
1 
...do. 
Bo. 
Incense cedar (Libocedrus decurrens ). 
1 
...do. 
Do. 
Redwood (Sequoia sempervirens ). 
1 
...do. 
Do. 
Bigtree (Sequoia washingtoniana) . 
I 
...do. 
Do. 
Bald cypress (Taxodium distichum) . 
1 
...do. 
Do. 
Yew (Taxus brevifolid) . 
1 
...do. 
Do. 
Arborvitse (Thuja occidentalism . 
I 
...do. 
Do. 
Western red cedar (Thuja plicata) . 
I 
...do. 
Do. 
Eastern hemlock (Tsuga canadensis ). 
1 
...do. 
Do. 
Western hemlock (Tsuga heterphylla) . 
2 
...do. 
Do. 
Black hemlock (Tsuga mertensiana) . 
1 
...do. 
Do. 
TYLOSELIKE CELLS 
The tyloselike epithelial cells which surround the resin canals were 
also carefully studied in Pinus, Larix, Picea, and Pseudotsuga. In these 
woods both the horizontal and vertical resin canals often contained dis¬ 
tended cells which partly or sometimes completely filled the canal 
openings. (PI. LVII, fig. 2; and PI. LVIII, figs. 2, 5, and 6.) This 
closed condition of the vertical canals is particularly noticeable near the 
medullary rays. (PI. LVI, fig. 1; and PI. LVII, fig. 2.) The distended 
closing cells correspond to the plasma-containing cells described on page 
446. (PI. LVIII, figs. 2 and 5.) A large number of the canals were, 
however, entirely open. 
In pines where many of the epithelial cells remain capable of growth, 
three types of conditions may be found in the canals. 
(1) The canals of the sapwood, especially of the outermost ring, may 
not have yet opened—that is, the space which the canal will occupy may 
still be filled by the parenchyma cells which later form the epithelium. 
(PI. LVI, fig. 1.) 
(2) Many canals may be partly open. (PI. LVII, fig. 1.) Frequently 
the cells surrounding the opening are somewhat contracted and col¬ 
lapsed; or, again, individual cells containing plasma may become dis¬ 
tended, bow out into the open lumen of the canal, and thus assist in 
partially closing it. 
(3) Canals in the heartwood as well as in the outer rings of the sap- 
wood may be completely closed. 1 This may come about in two ways: 
First, the groups of parenchyma cells observed in the sapwood may 
28736 0 —14-2 
1 Compare Thomson, R. B. 
