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



with the newly formed sclerenchymous layer behind F2 so as 

 to give a continuous stem rind with a deep inflection correspond- 

 ing to the one above noted on plane 14 to the right and back 

 of the Fl organ. The latter organ had become so greatly 

 reduced that it did not persist to the plane above, and is, there- 

 fore, represented as terminating at this level, as is also the 

 case with the P2 cluster. The P2' cluster had suffered no 

 material change, while the pZ" one had developed in width 

 and in the size of its component parts. 



As regards the features that enter into it from below, the 

 next plane (8) differs principally in the considerable develop- 

 ment of the p2" and the appearance of senile characters in the 

 P2' and F2 groups of strands. ISTew features are the scleren- 

 chymous band behind p2 ;/ on the left and the beginning of a 

 new (]?%") P cluster of strands on the right. 



On plane 7 the strong inflection of the rind in the plane 

 above has permitted the representation of what appears to be 

 a new feature {fl') that in reality (see fig. 2, B) had presented 

 itself on plane 14. Otherwise no great variation from the 

 plane below is to be noted. The ^2" cluster had united into a 

 single complicated strand which should here take the denomi- 

 nation of P2 // and which bears a striking resemblance to cer- 

 tain phases of the P strands in Psaronius brasiliensis, except 

 that its concave face is directed outward instead of inward. 

 This is the ear-shaped process of Count Solms-Laubach, who 

 interpreted it, as is done here, as a vigorous member of the 

 group to which it belongs, destined to supersede its senile 

 companions. 



At the level of plane 6, F2 and P2' were so near extinction 

 that they did not persist to the plane above ; f\! had emerged 

 laterally as FP in a manner similar to that above described for 

 /2-F2, and a new {p%"") P cluster had appeared on the left. 



The essential changes in the growth between planes 6 and 5 

 were the extinction of the F2 and P2 ; organs and an almost 

 complete extinction of the inflection of the stem rind behind 

 the former, corresponding to the similar change that took place 

 on the left in the growth between planes 10 and 8. 



To complete the figure, plane 2 instead of plane 1 has been 

 selected because the latter, being a fractured face, does not 

 show the structural features as clearly as does the cut and 

 polished one below it. The distance between the two planes 

 is so small that nothing of importance is lost by the resulting 

 shortening of the figure. On this plane the features of the 

 narrow frontal zone that could be represented on the planes 

 below, show that no material changes had occurred in their 

 growth upward from plane 5. Behind them appear an internal 

 sclerenchymous band that commenced to form at about the 



