78 



1111 OPHIOGLOSSALES 



the protoxylem .1 few scattered, large tracheary elements, so that the bundle may he 

 s.uil to be mesarch, .is Farmer states is the ease In the older rhizome. 



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

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

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

 thev are developed onlv in a \ei\ 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 

 Botrychtum lunarta, differing from that of B. virgimanum in the absence of a true 



Fig. 52. 



A. Section d( tin ^oung central stele of Hrlminthoitachxs, showing tin' two xylems. X200. 



IS. Stele from lower part of .in oldei sporophyte, showing junction of a leaf trace with central 6tele. 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 xvlem 

 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 /one which is so conspicuous in the stele of Botrychtum virgimanum. 



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

 stem apex downward, it appears that the cylindrical stele in H elmtnthostachyi 

 arises in precisely the same way as that of Botrychtum, viz, by the union of the leaf 

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

 in longitudinal section appears to he 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. 



