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 PL LIU, 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. (PL 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 (PL 

 LV, fig. 2) or it may be of medium thickness as in oak. (PL LIU, figs, 

 i 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 of ten produced, as in mesquite, maple, or cherry. 

 This gum usually collects in the vessels (PL LIU, 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 LIU, 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 



i * ' {^cfi lit z Glim Tni. ' ' 



