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



between planes 5 and 2 that they, and the strand groups 

 separated by them, were in the phase of development 

 corresponding to that shown on plane 14. 



The shading applied in fig. 3 to parts of the lower and 

 upper planes does not represent a natural feature visible in the 

 specimens, but is introduced to express diagrammatically the fact 

 that the strands enclosed by the shaded areas are interrelated 

 as component parts of the same organ, and not, as might be 

 supposed at first sight, an appreciable differentiation in the 

 parenchymous mass, represented by blank spaces, that surrounds 

 the vascular and sclerenchymous parts to which the drawing 

 has been limited. The differentiation that really exists but 

 that could not be represented without unduly complicating 

 the figures, is of two kinds of which only one is perceptible 

 macroscopically. This, which has been discussed in Count 

 Solms-Laubach's paper and is clearly shown in the photographs 

 that accompany it, consists of the segregation of a large part, 

 if not all, of the central parenchymous mass around the vascular 

 strands as an outer covering. This feature which I had pos- 

 tulated hypothetically in the study of the crown structure of 

 Psaronius brasilie?isis (this Journal, Aug. 1914), is more distinct 

 in the stem here considered than in any other Fsaronide known 

 to me, and it suggests a comparison with the closely appressed 

 leaf-stalk portions of the trunks of Tubicaulis and Thamnopteris. 

 The second differentiation established microscopically by 

 Count Solms-Laubach is that due to the filamentary character 

 of the parenchyma (Fiillgewebe) outside of the stem rind, in 

 the zone of the adventitious roots and of the emerged F 

 organs, in contrast with the ordinary type of parenchyma 

 within the rind. 



In figs. 1 and 2 the stem rind is shown diagrammatically 

 by simple thin lines, whereas its true appearance, better shown 

 in fig. 3, is that of a moderately broad band of tolerably 

 uniform thickness, except in the recesses occupied by the 

 emerge dF organs, where it tends to thicken and eventually 

 to become difficultly distinguishable from the broad parenchy- 

 mous mass that, after the extinction of the organ, lies between 

 it and the inner border of the root sheath. 



Eiode Janeiro, Oct. 20th, 1914. 



