78 



THE OPHIOGLOSSALES 



the protoxylem a few scattered, large tracheary elements, so that the bundle may be 

 said to be mesarch, as Farmer states is the case in the older rhizome. 



During its earlier stages the stele shows no leaf gaps where the leaf traces 

 depart, and the leaf gaps are only gradually developed. Soon after the stele has 

 assumed the form of a hollow cylinder the leaf gaps are for some time absent, or 

 they are developed only in a very small degree and close almost immediately upon 

 the departure of the leaf trace. 



In none of the young plants that I examined could I detect any of the inner 

 endodermis which occurs in the older rhizomes. Farmer, however, states that the 

 inner endodermis is only imperfectly developed and concludes that it is the result 

 of the invagination of the outer endodermis through the leaf gap; or, to put it in 

 another way, it is the persistence of the inner endodermis of the leaf traces of which 

 the hollow stele is made up. The bundle at this stage most nearly resembles that of 

 Botrychium lunaria, differing from that of B. vtrginianum in the absence of a true 



Fig. 52. 



A. Section of the young central stele of Helminthostachys, showing the two xylems. X200. 



B. Stele from lower part of an older sporophyte, showing junction of a leaf trace with central stele. X50. 



C. Part of central stele, more highly magnified. 



cambium, the outer wood cells being directly in contact with the inner cells of the 

 phloem. Occasionally, however, there may be seen on the outer edge of the xylem 

 ring a few imperfectly developed tracheids which probably represent a very rudi- 

 mentary development of secondary wood, but there is no other sign of the definite 

 cambium zone which is so conspicuous in the stele of Botrychium virginianum. 



From this study of the development of the leaf traces, following them from the 

 stem apex downward, it appears that the cylindrical stele in Helminthostachys 

 arises in precisely the same way as that of Botrychium, viz,Jby the union of the leaf 

 traces. The appearance of procambium upon the ventral side of the stele, which 

 in longitudinal section appears to be derived directly from the stem apex, can thus 

 be explained by the ventral extension of the broad leaf traces which meet on the 

 lower side of the stem as well as above, and the cylindrical stele is thus developed. 



