The Trees of Vermont 199 



one kind of cells, tracheids, as is the case in the coniferous woods just 

 mentioned, the wood of broad-leaved trees is composed of several 

 kinds of cells. If we examine the cut end of a red oak branch we 

 notice that the spring wood contains many comparatively large open- 

 ings which are visible even to the naked eye. These openings are called 

 pores ; they are cross-sections of open tubes or vessels or tracheae 

 which run up and down the trunk of the tree and out into the branches 

 and twigs. In the beginning they resembled the tracheids of conifers, 

 i. e., they were made up of separate and distinct cells. Later, the end 

 walls of the cells which met endwise were absorbed, leaving a con- 

 tinuous series of connected cells or a tube (c, fig. IX). These tubes 

 or vessels serve in the living tree as water-carriers. For the sidewise 

 conduction of fluids, the vessels are usually abundantly pitted with 

 bordered pits, but the pits are somewhat smaller than those commonly 

 found in the tracheids of coniferous woods. Furthermore, it is very 

 common for vessels, especially the smaller ones, to be marked with 

 spiral thickenings on their interior walls. The scalariform perfora- 

 tions present in the end partitions of the vessels of a few woods, as 

 seen on the radial-section, are sometimes confused with the true spiral 

 thickenings just mentioned. This point may be definitely determined 

 by an inspection of tangential- as well as radial-sections. Tyloses 

 also occur in the vessels of many of the broad-leaved woods, sometimes 

 being visible to the naked eye. Tyloses are usually rather thin-walled 

 cells which protrude into the cavities of the vessels, where they divide 

 rapidly and grow, sometimes filling the entire cavity and plugging the 

 vessels so as to prevent further conduction of fluids. The value of 

 white oak for cooperage is increased by tyloses, which are especially 

 abundant in the vessels of this wood. They are also well-represented 

 in the locust, in this instance being rather thick-walled. 



It is convenient to divide broad-leaved woods into two groups, 

 which are characterized by the size and arrangement of the vessels. 

 In some species of wood the vessels which are formed later in the 

 season are much smaller than those formed earlier. A wood of this 

 kind, with its large pores collected into a row or band in each growth 

 ring, is spoken of as ring-porous. In other woods, the pores are more 

 nearly uniform in size in both spring and summer wood. They are 

 designated as difl^use-porous woods. The wood of the maple is of thi= 

 character. In many of the diffuse-porous woods the pores are toe 

 small to be seen with the naked eye, and in some cases they may even 

 be indistinct when viewed with a lens. Thev should not, however. 



