0. A. Derby — Stem Structure of Tietea Singularis. 255 



while the P and C (seen only on the upper face) ones are sim- 

 ply outlined. The groups of strands on the different faces are 

 hypothetically joined by heavy dotted lines for the F and by 

 lighter lines for the P ones. The spacing is based on the 

 thickness of the various slices with an allowance of 2 mm for the 

 saw cuts, except in the case of the interval between 7 and 6, 

 from which a thin slice for microscopic preparations had evi- 

 dently been taken before the three parts of the original speci- 

 men came into my hands to be forwarded to Count Solms- 

 Laubach. Whether too great or too little space has been given 

 to the saw cuts makes no material difference in the general 

 accuracy of the plotting. 



Beginning with the basal (14) section of A in fig. 2 the front 

 of the trunk and the cross section of the root sheath are shown, 

 but above this plane these features are discontinued and only 

 those of the stem proper are plotted. Behind the stem rind 

 lies, at the center and right, an elongated group of P strands 

 which are interpreted as belonging to an older (P2) and a 

 newer (P2') cluster which, coming up from below, were here in 

 a senile and a youthful stage of growth respectively, the latter 

 cluster being backed by a long curved sclerenchymous band. 

 To the left of this group the stem rind describes a deep sig- 

 moid curve, shown by a dotted line behind its extreme left 

 end, and then extends in a straight course to the margin of the 

 figure. In the deep broad indentation formed by this inflection 

 of the rind on the outer surface of the stem, lies a many-stranded 

 F organ which is here cut in a fully developed stage of growth, 

 while behind it and inside the rind a row of small strands 

 representing the embryonic stage of the p2 r/ cluster had 

 appeared. 



On the next plane above (12) a tendency towards extinction 

 is shown in the inflection of the stem rind at the left as well as 

 in the P2 and Fl groups of strands, and towards development 

 in the jpV group ; but otherwise the features above enumerated 

 are not materially changed. The/12 group, which in the draw- 

 ing appears as a new feature, is really distinctly developed on 

 the plane below, but its situation is so far in the background 

 that it could not be represented. 



On plane 10 are registered important modifications intro- 

 duced in the growth from the plane below. At the right the 

 immature f% organ had developed into the adult (F2) stage of 

 growth and had emerged laterally through the interruption, 

 by its overlopping, of the stem rind in front of it, accompanied 

 by the formation of a sclerenchymous layer behind it. Accom- 

 panying this change the internal sclerenchymous band of the 

 lower planes swung around in a complicated curve to unite at 

 its right border with the interrupted stem rind and at its left 



