Mar. 25, i 9 i 4 Tyloses in American Woods 451 



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 

 UII, 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. (PL UX, fig. i .) 



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 UV, R2, and by some of those in Plate 

 LV, figure i . 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 lobata), 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 

 figures 1,2, and 3, and LV, figure 2. 



