XIX] ANATOMY 55 



progression from a more robust type of cellular construction as seen in Eu- 

 sporangiate Ferns, to a less robust as seen in Leptosporangiate Ferns, 

 characterised by definite and regular segmentation. The meristematic 

 characters of the Ophioglossaceae, though not very distinctive, rank most 

 nearly with those of the Marattiaceae. In them, as will be shown later, 

 the young and slender parts may often have a single initial, though its iden- 

 tity is lost in the adult. But the sporangial structure is quite distinctive of 

 a primitive state: and what is seen in Eqiiisetum shows that a typically eu- 

 sporangiate plant may yet have a single initial with very regular segmentation 

 in its stem and root; this is so also in the Ophioglossaceae. The general con- 

 clusion is that the Ophioglossaceae fall in with certain other Eusporangiatae 

 in their apical constitution. On the other hand, the only direct basis for 

 comparison with the Botryopterideae is through Kidston's specimen of the 

 leaf-tip of Zygopteris corrugata (Vol. I, Fig. 104, p. 109), which shows an 

 apical structure quite comparable with what might be seen in a modern 

 Botrychium. This is in itself interesting, but the fact should not be accorded 

 any undue importance. 



Vascular Anatomy 



The Ophioglossaceae have as a rule naked surfaces when mature, but 

 sparse hairs may be found near the stem-apex, and especially in O.palmatuni. 

 They are mostly sappy, soft-tissued plants, and their ground tissue, being 

 used for storage and other purposes, does not present features of compara- 

 tive value. Accordingly the interest centres round the vascular system. 

 Following the general view above stated, Botrychium and Helminthostachys 

 will be considered first, and OpJiioglossum will subsequently be compared 

 with them. 



The Root 



The roots are hairless: their massive cortex, which is commonly used for 

 storage, is delimited from the central stele by an endodermis of a relatively 

 primitive type (Fig. 347). The stele is of a quite usual construction: in 

 Helminthostachys it is frequently hexarch or even heptarch: in B. virginia- 

 num it may be tetrarch or triarch, but in most species of Botrychium and 

 Ophioglossum it is diarch or even monarch. Most of the species of Eu-Ophio- 

 glossum have monarch roots, and this is conspicuously the case in O. vulga- 

 tuiii. In 0. Bergianuiu the structure may be diarch or monarch, the latter 

 having been observed in roots close to their base (Fig. 348). With the 

 monarch structure goes terminal bifurcate branching, while monopodial 

 branching is seen where the structure is more complex, as in O. pejidu/um, 

 Botrychium, and Helminthostachys. Thus both dichotomous and monopodial 

 branching are found in the same genus. Possibly dichotomy is restricted to 



