Mar. 35,1914 
Tyloses in American Woods 
459 
bordered pit. Such growths are termed “tyloselike,” since they produce 
an effect very similar to that produced by the true tyloses of the hard¬ 
woods. 
Resin canals or ducts are normally present in the following coniferous 
genera: Inarch, or tamarack (Larix), spruce (Picea), Douglas fir (Pseu- 
dotsuga), and pine (Pinus). These canals when seen in cross section 
often bear a superficial resemblance to the vessels or pores of the hard¬ 
woods. (Pl. LVII, fig. 1.) They are, however, different in both their 
origin and function. Resin ducts are not cellular elements, but simply 
intercellular spaces which result from the splitting apart of the common 
walls of a group of parenchyma cells. A very early stage of this splitting 
is shown in Plate LVI, figure 1. These parenchyma cells which surround 
the canal opening are called “epithelial cells/’ They are the seat of 
resin formation, and they cause the tyloselike closing of the resin canal. 
Certain of them often remain thin walled and contain plasma. (PI. LVIII, 
figs. 2 and 5.) After they split apart to form the canal, when they change 
in shape and size, a further swelling and growth may take place which 
closes the canal entirely or in part. (Pis. LVII, figs. 1 and 2, and LVIII, 
figs. 2, 5, and 6.) The fact that it is the growth or expansion of the 
whole cell, and not a portion of the wall of that cell, together with a 
portion of the wall of the neighboring cell, as in the tylose-forming 
membrane of the one-sided bordered pits of the hardwoods, clearly 
indicates the difference between the true tyloses of the hardwoods and 
the tyloselike cells in the resin canals of the conifers. 
OCCURRENCE) OF TYLOSES AND TYLOSELIKE CELLS IN NATIVE 
CONIFERS 
Over 600 permanently mounted sections from coniferous woods in 
the collection of the Forest-Products Laboratory were specially studied, 
while more than three times this number were examined unmounted. 
true tyloses 
Ray or true tyloses were found in the normal wood of the conifers, 
but were not abundant. Their shape and general appearance are well 
illustrated in Plate LVI, figures 1 and 2. None of the long, saclike 
vesicles which sometimes fill the whole tracheid lumen in the roots of 
conifers were found. The greatest development of true tyloses was 
found in the soft pines. In this group they were better developed in 
spring wood than in summer wood and were more numerous in the sap- 
wood than in the heartwood. Indeed, some of the pit membranes in the 
heartwood were concave in shape, appearing to have collapsed inward 
instead of protruding into the tracheid. 
The size of the pits between the medullary ray cells and the tracheids 
in conifers bears a definite relation to the formation of tyloses. As a 
rule, the ray pits in the hard pines are small and tyloses are lacking, 
