CH. XIX] 



HABIT 



43 



vertical in the sporeling, 



Slim, but in HelviintJiostachys, though its axis is 



there is a creeping rhizome in the 



adult, and the leaves are disposed 



in two rows on its upper surface. 



These facts point to an upright 



radial stock as the original form 



for them all, though it is departed 



from in i\ie3.dn\t Heluiiuthostachys, 



in which the shoot is dorsiven- 



tral. 



The form of the sterile leaf-blade 

 defines the three genera. In Hel- 

 minthostachys it is usually ternate, 

 each of the divisions being again 

 divided : the venation is open (Fig. 

 335, E). In Boiiychium the blade 

 is variable in outline: in the small- 

 est it may be simple and un- 

 branched, in others it may be 

 simply pinnate, as in B. Lunaria; 

 or it may be doubly, trebly, or 

 even four times pinnate, as in B. 

 virginianuiii: but still the venation 

 is always open (Fig. 335, D). This 

 is in strong antithesis to the re- 

 ticulate venation of Op/noglossum, 

 in which the leathery blade is 

 usually entire (Fig. 336, C), though 

 in some species it may be irregu- 

 larly lobed. Reticulation of the 

 veins is general for the genus, and 

 it is found even in the minute 

 sterile blade of O.Bergianum. This 

 is held to be a more advanced 

 state, and being combined with 

 other features it suggests that in 

 OpJiioglossinn we see a later and 

 derivative type of the Family. 

 Botrychiuni and HelminthostacJiys 

 will therefore be described first. 



In the genus Botrychhtm the short upright stock is sheathed by the dry 

 bases of the older leaves, and is usually unbranched. The plant is mono- 



Fig. -3,^^. C, Ophioglossuni zndgatjtni L., the sterile 

 blade, showing reticulate venation. Z>, Botrychiuin 

 Limaria Sw. , sterile blade showing open dicho- 

 tomous venation. E, Helminthostachys zeylanica 

 Hook., a single lateral segment of the sterile blade, 

 showing open dichotomous venation. (Natural 

 size.) (After Diels, from Engler and Prantl.) 



