2 go 



BOTANICAL GAZETTE 



[OCTOBER 



present Osmundaceae from a protostelic group. It becomes 

 particularly significant when we observe that Kalesskya and Tham- 

 nopteris were characterized by traces which departed in a proto- 

 stelic manner and were strongly mesarch until they had entered 

 for some distance into the petioles, where the xylem opened out 

 and presented an appearance like that in the rachis of Osmunda 

 and Todea. As already stated, these early representatives of the 

 Osmundaceae were present in the Upper Permian and much pre- 

 ceded the Lower Cretaceous siphonostelic species Osmundites 

 skidegatensis to which Jeffrey (7) referred for the most primitive 

 type of osmundaceous stele available. The recurrence of mesarch 

 strands, abnormal central tracheids, and a typical protostele in 

 the young stem of Todea are interpreted as indicative of the descent 

 of our present Osmundaceae from a protostelic ancestry. 



Summary 



1. The young sporophyte of Todea barbara is protostelic. 



2. Preceding the departure of the early traces one o 



more 



parenchyma cells appear in the xylem group, or occupy a groove 

 which is in contact with the sheath parenchyma. These, at the 

 time of isolation of the trace from the central cylinder, become 

 confluent with the xylem sheath, leaving the stele solid, or grooved 

 opposite the strand. This depression is continuous up the stem, 

 where it either becomes more shallow and is lost, or detaches one 

 or more parenchyma elements which become centrally placed in 

 the xylem group where they end blindly, or are in continuity with 

 parenchyma decurrent from the succeeding trace. 



3. The stem meristematic tissue is derived from a single apical 



- 



cell of the triangular-pyramidal type. It, like the root initial, 

 shows variation in the order of segmentation. Only one instance 

 not certainly referable to a single initial was found. 



4. Roots originate from the pericycle in the young sporophyte 

 and very early develop a single apical cell which is broadly tri- 

 angular and pyramidal, characterized by variation in shape and 

 order of segmentation. Segments are large and frequently give 

 the appearance of two or more apical initials. All root meristems 

 examined, how T ever, were referable to a single initial. 



* 



