92 



THE OPHIOGLOSSALES 



of the Stem, which is identical in appearance in the cortical and the central regions. 

 The bundle from each young leaf can be traced to a junction with a root stele and 

 from this point of junction it extends through the ground tissue of the stem, running 

 almost horizontally until it joins the trace from the next older leaf. In this way is 

 built up the open, large-meshed vascular cylinder. So far as could be determined 

 in O. moluccanum only one root was formed for each leaf. The tissues of the root 

 base are continued upward to connect with the young leaf and downward to join the 

 stele from an older one. 



No endodermis can be detected in the bundles of the stem in 0. vulgatum and 

 the same is true for 0. moluccanum, but in O. bergianum, 0. capense, and O. elltp- 

 ticum, according to Poirault (Poirault 2), both an inner and outer endodermis occur 

 in the older part of the rhizome; these however, disappear in the younger region 

 higher up. 



A transverse section of the mature rhi- 

 zome (fig. 57) in Ophtoglossum. moluccanum 

 shows the widely separated sections of the 

 strands of the vascular cylinder as a circle 

 of small collateral bundles without any 

 endodermis, the mass of wood being in 

 immediate contact with the thin-walled 

 parenchyma of the ground tissue or sepa- 

 rated from it at most by a single row of 

 pericycle cells. In some of the smaller 

 species the leaf traces are relatively broader 

 and there is an approximation to the ring- 

 shaped section presented by the cylindrical 

 stele of Botrychium or Helminthostachys, 

 and sometimes the same appearance may be 

 approached in sections of the older rhizome 

 which happen to pass through a region 

 where there are numerous anastomoses of 

 the bundles forming the reticulum (fig. 57, E). 



Except for the vascular bundles, the 

 tissue of the stem is made up almost ex- 

 clusive]}' of simple parenchyma. The de- 

 velopment of periderm, which takes place 

 to a limited extent in the outer region, is 

 doubtless associated with the old leaf bases, 

 as it is in Botrychium. 



The leaf structure of Euophioglossum is 

 exceedingly simple. The mesophyll is made 

 up of thin-walled green cells, practically uni- 

 form throughout; and through this spongy mass of mesophyll the delicate veins pass 

 without forming any projections at the surface. Both sides of the leaf are provided 

 with a simple epidermis, stomata being developed on both sides of the leaf. In 

 those species in which the leaf lies more or less horizontally, as it does, for example, 

 in O. reticulatum ^ the stomata are less numerous upon the upper surface. 



The arrangement of the bundles in the petiole has been already studied in the 

 commoner European species, 0. vulgatum and 0. lusitantcum. In all of the species 

 belonging to the section Euophioglossum there is given off from the vascular system 

 of the rhizome a single leaf trace, which divides at the base of the leaf into two 



Fig. 58. 



Longitudinal section of a sporophyte of Ophioglossum 

 moluccanum, older than the one shown in fig. 56. X20. 



