[PENHALLOW] A REPORT ON FOSSIL PLANTS 299 
the parenchyma elements within such tracts often conspicuously re- 
sinous. Medullary rays prominent, numerous, upwards of 4 cells 
wide, sparingly resinous. 
Radial.—Ray cells all of one kind, low and more or less contracted at the ends; 
the upper and lower walls thin and not pitted; the terminal walls 
sometimes thick and strongly pitted; the lateral walls without obvious 
pits. Vessels of the spring wood broad and short, 1% to2 times longer 
than broad, the radial walls with multiseriate, hexagonal pits with 
large, transversely oblong pores; the smaller vessels fibrous, but with 
similar construction, the pits often reduced to a single row; thyloses 
of the large vessels often strongly developed, but more or less strictly 
localized. 
Tangential—Rays numerous, medium, upwards of 4 cells wide; the small, 
rounded-hexagonal cells forming a dense structure. Vessels as in 
the radial section. 
250 TLMUS COLUMBIAN 
= of 19033. ULMUS COLUMBIANA, D. sp. 
Plate VIII. 
Among the woods represented in the collections of 1903, was a 
specimen believed to be a new species of Rhamnacinium, and provision- 
ally referred to that genus under the number ae A more critical 
examination proves it to be an elm of a type not readily assignable to 
any known species. Its diagnosis is as follows :— 
Transverse.—Growth rings rather broad and well defined. Tracheids not very 
thick-walled, gradually passing into a thin and poorly defined 
limiting zone upwards of 8 tracheids thick. Medullary rays numer- 
ous, 1-4 cells wide, resinous, distant chiefly one but sometimes three 
rows of vessels. Vessels oval or round, more or less in radial rows, 
radially 1-5 seriate or sometimes tangentially 2 seriate; the larger 
vessels occupying a zone of variable width in the spring wood and 
often preceded by a series of smaller vessels, more or less abruptly 
diminishing and becoming more scattering toward the summer wood 
where they form more or less scattering groups or finally become 
merged with the wood parenchyma. Wood parenchyma very variable 
and often apparently wanting, but when prominent surrounding groups 
of vessels or forming isolated and commonly tangentially disposed 
tracts of variable size near the outer limits of the growth ring. 
Radial.—Vessels short and commonly broad, the hexagonal, multiseriate pits with 
transversely slit-like pores. Medullary rays numerous and medium to 
rather high, the cells all of one kind though often much shortened: the 
upper and lower walls rather thin, or in the short cells thick and 
much pitted: the lateral walls multiporous when contiguous to vessels. 
Vessels of the medullary sheath spiral and scalariform, the adjacent 
parenchyma filled with starch. Wood parenchyma cells about eight 
times longer than broad. 
