0. A. Derby — Stem Structure of Tietea Singularis. 251 



Art. XVI. — Illustrations of the Stem Structure of Tietea 

 Singularis ; by Orville A. Derby. 



[Preliminary note in advance of the " Annaes do Servigo Geologico e Min- 

 eralogico do Brazil."] 



Under the name of Tietea singularis Count Solms-Laubach 

 recently described and illustrated (Zeitschrift fur Botanik, Y, 

 pp. 673-700) a fragment of fossiPwood of Permian age from 

 the state of Sao Paulo, Brazil, which he found to present a 

 variation from the Psaronius type of structure sufficiently 

 important to justify a new generic denomination. Having tem- 

 porarily in my possession the different slices into which the 

 original specimen was cut, it seemed desirable to utilize the 

 exceptional skill of Mr. Francisco Basto in the construction of 

 general plots showing in a connected whole the essential struc- 

 tural features so ably worked out by the author of the genus 

 and species, but which are of too complicated a character to be 

 made readily comprehensible by a written description and 

 isolated figures of a part of the cross sections. 



The task proved an exceedingly difficult one, more especially 

 in the matter of finding a satisfactory mode of representation, 

 owing to the occurrence in a small space of a great number of 

 individual strands belonging to different groups and arranged 

 in successive ranks like a military troop on parade in close 

 order. The process employed was to trace carefully with ink 

 on photographs the vascular and tegumentary systems and then 

 to wash out all the uninked parts of the photograph. A series 

 of skeletonized cross sections were thus obtained and from these 

 the features to be represented were transferred to the drawing 

 by the processes of mechanical draughting, so that the imagina- 

 tion of the artist only came into operation in the joining up 

 of the successive cross sections across the intervening concealed 

 spaces. Fortunately the cross sections were so numerous and 

 had been so judiciously spaced by Count Solms-Laubach, under 

 whose direction the cutting was done, that the few cases of 

 doubt regarding the course of a given strand from one plane 

 to another could only affect questions of minor importance. 

 On the completion of the work, which was done under my con- 

 stant personal supervision but without any botanical preconcep- 

 tions whatsoever, it was very gratifying to find that in the 

 most essential particulars the result was a graphic representa- 

 tion of Count Solms-Laubach's written summary of the struc- 

 tural features of the stem. 



The specimen which contains parts of two vertical rows of 

 F organs is evidently a fractional portion of a polystichous 

 stem which if approximately circular in outline would have 



