SUPPORTS 261

though larger than the other cells, are not so conspicuous as in the ring-porous
group. There is only a gradual, not a marked, decrease in size from the spring-
wood to the summer-wood pores. Tylosis is the name given to froth-like growths
which fill the pores of certain hard-woods. A. Koehler (Guidebook, etc., p. 5)
says, * These are formed by ingrowths from neighboring cells and fill the pores

o?gro^

o ' " '°° °*

P^^o o * o

•O *•"' £S O A <? f

J Q ^y Q O__ Q __ t*

Q

O

^?^^ ° o c 5 b

° « ° « o . «

FIGURE 4. Diagrams adapted from those in Guidebook for the Identification of Woods
Used for Ties and Timbers^ by Arthur Koehler (Washington, D. C.: Government Printing
Office, 1917). These are from figures 3 to 6. At a is shown a cross section of ring-porous
wood with a radial arrangement of pores in the summer-wood; at b a similar section
with a wavy, tangential arrangement of the summer-wood pores; at c a ring-porous
wood without any definite arrangement of the pores in the summer-wood; and at d a
diffuse-porous wood.
more or less like so many toy balloons crowded into an air shaft.* Parenchyma
cells make up the light-colored tissue that can be seen between the pores of hard-
woods. The distribution of the parenchyma is useful in identifying woods.
2-. Soft-woods or conifers have no pores, *'.<?., specialized cells of the type
distinguishing the hard-woods. Instead, they have fibre-like cells (tracheids)
with closed ends. Not all the soft-woods are actually very soft. These woods come