Mar. 25,1914 
Tyloses in American Woods 
449 
These three types of arrangement and the degree of their development 
bear a definite relation to the development of tyloses, since they indicate 
whether the parenchyma cells are near enough to the vessel cavities to 
send their prolongations into them. In addition to the wood paren¬ 
chyma, the position and number of the medullary rays adjacent to the 
vessels must be taken into account. A grouping of the species of wood 
with the twofold object of indicating the distribution of tyloses and the 
arrangement of the wood parenchyma clearly brings out some of the 
reasons why tyloses are so much more abundant in certain woods than 
in others. Wherever the paratracheal or vasicentric type of parenchyma 
is well developed, the tendency for marked tylose formation, or else for 
gum production, is very noticeable. From Table I it is further evident 
that when tyloses are strongly developed either paratracheal or abundant 
metatracheal parenchyma is always found. 
SHAPE, THICKNESS OF WALL, AND CONTENTS OF TYLOSES 
The shape of the tylosal projections varies widely. They are some¬ 
times spherical, or again they appear as elongated vesicles. (PI. LII, 
fig. 3; and PI. LIII, figs, i, 2, and 3.) Often when the walls are very 
thin they appear much collapsed and wrinkled as, for instance, in ash 
or the wound tyloses in cow oak. (PI. LIV, Ri.) The extent to which 
the tylose wall increases in thickness varies also. The wall may be an 
extremely thin delicate membrane as found in ash or osage orange (PI. 
LV, fig. 2) or it may be of medium thickness as in oak. (PI. LIII, figs. 
1 and 2.) 
The contents of the tyloses are in general the same as those of the paren¬ 
chyma cells producing them. Starch is common, and resin, calcium 
crystals, and gums have also been observed. 
When normal parenchyma cells do not give rise to tyloses, the so-called 
“gums” (Prael) 1 are often produced, as in mesquite, maple, or cherry. 
This gum usually collects in the vessels (PI. LIII, fig. 4) and parenchyma 
cells. In the vessels it sometimes assumes the form of globules or drop¬ 
lets which may easily be mistaken for tyloses. In order to determine 
whether gum or tyloses are present, a section of the wood may be treated 
with some gum solvent, such as absolute alcohol or caustic soda. When 
the wood is dry, the gum droplets are often characteristically cracked 
and split. Their general appearance is illustrated in Plate LIII, figure 4. 
MATERIAL AND METHODS USED IN THE STUDY 
The material used for this study of tyloses was a collection of logs of 
commercial size from native-grown trees. As a basis for the study of 
tyloses this material was unique, since most of the work of other inves¬ 
tigators has been done not on wood from the bole of the tree, but on 
1 “ Schutzgummi. 
