Mar. 25, 1914 
Tyloses in American Woods 
45i 
found to check reasonably well, as shown in Table II. The greatest 
variation occurs in the species in which tyloses are very rare or else 
scatteringly developed and, therefore, where their practical importance 
is relatively slight. 
OCCURRENCE OF TYLOSES IN NATIVE HARDWOODS 
Table II gives the results of observations made on the distribution and 
region of first development of tyloses in 143 specimens of hardwoods 
grown in the United States. The very marked development of tyloses 
in certain species has been noted in Table I. 
Special attention was given to the early development of tyloses. The 
results show their presence in the sapwood of all the species in which 
they occur in the heartwood. The hickories, for instance, give some 
interesting data concerning the occurrence of tyloses in sapwood. It 
has been maintained that if tyloses ever occurred in sapwood they would 
be found only in very narrow sapwood—that is, where the transition from 
sap to heartwood begins at the end of the first or second year after the ring 
is formed, as, for instance, in some of the oaks. In the hickories, however, 
tyloses are always present in the sapwood, and are generally developed 
even in the outermost rings as abundantly as in the heartwood. Plate 
Till, figure 3, shows a cross section of the sapwood of pignut hickory 
(Hicoria glabra ), including the fourth to the seventh rings in from the bark. 
This particular tree had 31 rings of sap, or uncolored wood, and tyloses 
were well developed in the very outermost rings. (PI. LIX, fig. 1.) 
Tyloses are normally lacking in the red-oak group, although there are 
many exceptions. An illustration of vessels not filled by tyloses is given 
by those in the middle of Plate LIV, R2, and by some of those in Plate 
LV, figure 1. In some cases tyloses occur in individual vessels in species 
ordinarily free from them, as Spanish oak. (Table II.) In several instances 
the few scattered tyloses present in both the sapwood and heartwood 
have a rather abnormal appearance and are associated with areas of 
fungous growth. (Table II, Scarlet oak.) In certain species of the red- 
oak group, however, as blackjack oak (Quercus marilandica ), tyloses are 
very generally developed in both the sapwood and heartwood. 
In the white oaks, in contrast to the red-oak group, tyloses are generally 
very abundant, even in the outermost rings. Some of the white oaks 
where tyloses are slow in forming show striking examples of the growth 
and development of the tylose in its early stages. This is illustrated in 
Plate LII, figure 3, which is a reproduction of a photomicrograph of a 
cross section of California white oak, or valley oak (Quercus lobaia ), show¬ 
ing a piece of the sapwood next to the bark. Fragments of the bark may 
be seen at the top of the illustration. The relatively small bladderlike 
cells here shown increase in size until they grow together and fill the 
vessels as shown at the bottom of this illustration and in Plates LIII, 
figures 1, 2, and 3, and LV, figure 2. 
