RECORD: STRUCTURE OF CERTAIN WOODS 205 
short segments are found which appear to be subdivisions. The 
wood parenchyma strands show a uniformity in length with the 
vessel segments, but in a few cases where parenchyma is scanty 
the vessel segments and tracheids (when present) seem to be en- 
tirely responsible for the ‘‘ripple marks.” This was found to be 
the case in Dalea spinosa Gray, Artemisia tridentata Nutt., and 
Bigelovia graveolens Gray. 
The number of parenchyma cells per strand is not constant 
but in most of the woods investigated was found to be two or 
four; sometimes only one (an intermediate or substitute fiber). Itis 
not uncommon to find that the metatracheal strands are composed 
of two cells and the paratracheal of four. Where the parenchyma 
is abundant, the component cells of the strands may be uniformly 
disposed and thus give rise to a secondary seriation which, es- 
pecially if the cells are large, is readily visible under the lens. In 
this case the height of the tiers in only one half or one fourth that 
of the ordinary tiers. In species of Bombax, Ceiba (Eriodendron) 
and Heliocarpus the number of cells per strand is four; in Char- 
pentiera, Diphysa and Lonchocarpus, two; in Gossypium and Ptero- 
cymbium, two in the metatracheal and four in the paratrachea'. 
The same structure obtains in some of the finer-textured woods, 
but the small size of the cells usually renders it indistinct or in- 
visible under the lens. It was found fairly distinct in Ichthyo- 
methia piscipula (L.) Kuntze (mostly two cells per strand) and 
less so in Tabebuia Guayacan Hemsl. (four cells per strand). 
The libriform fibers and fiber-tracheids (collectively, wood 
fibers) may or may not show distinct seriation in the tangential 
section. In all ordinary cases the fibers are much longer than the 
vessel segments or the height of the tiers. In many cases there 
is a widened middle portion equal to about one third of the total 
length of the fiber and corresponding to the length of the original 
cambial cell. The attenuated ends of the fibers of one tier are 
forced during elongation between the fibers of the tiers immediately 
above and below and, in consequence, a cross section through the 
middle portion of a tier will show (under the compound micro- 
scope) alternate rows of large and small cells, the latter being twice 
as many as the large ones. A section through the junction of two 
tiers will show fewer cells and they will be more nearly uniform 
as 
