98 VASCULAR CRYPTOGAMS 



venter is completely imbedded in the prothallium, its wall being de- 

 veloped out of the tissue of the latter. 



The course of development of the embryo and rudimentary sporo 

 phyte has not yet been followed out in a sufficient number of instances 

 to warrant a general description ; in those in which it has at present been 

 observed it appears to present some discrepancies. 



The short stem is erect and entirely glabrous, often with a swollen 

 tuberous base ; only in Helminthostachys (Kaulf ) is there a creeping 

 anderground rhizome. In only a very few exceptional cases does it 

 branch. The flattened apex of the stem consists of an irregular meristem 

 derived from a single pyramidal apical cell. The fundamental tissue of 

 the stem consists of short nearly cylindrical thin-walled succulent cells, 

 which are longer in the leaf-stalk, interspersed with large intercellular spaces. 

 It exhibits a striking difference from the corresponding tissue of true ferns 

 in the entire absence of sclerenchymatous layers. It is separated by the 

 ' vascular ' cylinder into a cortical and a medullary parenchyme. It has an 

 epiderm well provided with stomates, and exhibits sometimes a remarkable 

 development of layers of cork. The ' vascular ' bundles form (in Ophio- 

 glossum vulgatum, L.) a hollow cylindrical network, from each mesh of 

 which is sent out a leaf-trace. The whole of the tissue which fills up 

 the meshes is frequently transformed into scalariform tracheides, so that 

 considerable lengths of the stem then contain a continuous hollow 

 cylinder of lignified tissue. The bundles of the stem are collateral, the 

 xylem occupying the axial, the phloem the peripheral side ; and the 

 structure is the same in Botrychium (Lunaria). Those of the leaf-stalk 

 are four to eight in number, arranged in a circle and separated by fun- 

 damental tissue. In Ophioglossum they are collateral, the axial portion 

 consisting of narrow reticulate tracheides, the peripheral portion of a 

 broad band of phloem, containing sieve-tubes ; while in Botrychium 

 they are concentric, consisting of a broad band of scalariform or reticulate 

 tracheides surrounded by a thick layer of phloem. There is no bundle- 

 sheath in Ophioglossum, and only a rudimentary one in Botrychium. 



The roots of Ophioglossacese are remarkable from the slight develop- 

 ment of the root-cap, and the absence of root-hairs. They spring from 

 the short stem in the midst of the leaf-insertions, and rarely branch, then 

 always monopodially. Like the stem, they originate from a single 

 pyramidal apical cell. The roots of Ophioglossum give rise to adven- 

 titious buds. 



The leaves are always very few in number, often only one on each 

 stem, and the number is uniform in the same species. They are re- 

 markable for the slowness of their growth, which extends, in Botrychium 

 Lunaria, over five years, the leaf only rising above the surface of the 



