320 ANNUAL REPORT SMITHSONIAN INSTITUTION, 192 8 



3. STRUCTURE OF GILBOA TREES 



A full, technical description of the Gilboa trees may be found in a 

 previous article by the writer (N. Y. State Mus. Bull. 251, 1924, pp. 

 50-93) by those who care to go into more detail than is given in the 

 following description. 



The stumps taken from the three horizons show great variability 

 in size and some variability in shape. (See pi. 5, figs. 1 and 2.) 

 The bases of the stumps are bulbous, as might be expected of certain 

 trees growing under swampy conditions, and show a circumference 

 at the base from 3 feet and less up to nearly 12 feet (diameter less 

 than 1 foot to nearly 4 feet). In general, the height at which the 

 trunks were broken off varies from a few inches over 1 foot to about 

 3 feet or slightly over, but in the spring of 1925 a large specimen 

 was taken from Riverside Quarry, which extended up into the trunk 

 for 5^ feet. Some of the stumps narrow quite gradually from the 

 bulbous base into the trunk, others very abruptly. The parts of 

 trunk above the heights shown in the stumps, which have been found 

 infrequently, are in a flattened condition. The museum has two 

 of these specimens, one over 4 feet long and the other over 3 feet 

 long. In the case of the latter, which was taken from the underside 

 of an overhanging ledge, as much again of the trunk had been broken 

 away and lost; and, beyond the section obtained, the trunk continued 

 into the solid rocks with little, if any, diminution in width. Another 

 specimen, too poor to be removed from the rock, showed some 12 feet 

 of slender trunk which must represent a portion near the top of a 

 large trunk or the trunk of a very small tree. Judging from the 

 stumps and the portions of trunks, the largest of these trees must 

 have reached heights of 30 to 40 feet. 



The outer cortex is the only structure of the stumps and trunks of 

 these trees that is to any extent preserved. The interior structures 

 have been washed out and the cavity left filled with sand which has 

 helped preserve the shape of the stumps in fossilization. The struc- 

 ture of the outer cortex is similar to that seen in a group of Carbon- 

 iferous seedferns {Lyginopteris^ Heterangiuin). It consists of inter- 

 lacing strands of strengthening tissue (sclerenchyma) , forming a 

 network, or more or less parallel (see pi. 6, fig. 1). In transverse 

 sections, unlike the Carboniferous forms, the sclerenchyma appears 

 in the form of dots or short thick irregular lines, irregularly scat- 

 tered. This zone of the outer cortex varies from an inch or less to 

 several inches in thickness, depending upon the size of the stumps. 

 In the majority of cases, the outside portion of the outer cortex is 

 missing, but it is well shown in several cases. The outer surface is 

 marked with shallow ridges and furrows, in some cases giving the 

 effect of a bark; in other cases the outer surface is only irregularly 



