382 



PART III. THE CLASSIFICATION OF PLANTS. 



and by the schizostelic structure of the stem with collateral vascular bundles ; 

 the stem is also gamodesmic in Botrychium and Helminthostachys, which thus 

 resemble Equisetum silvaticum (see Fig. 116), whilst Ophioglossum resembles 

 Equisetnm litorale. There is a single three-sided apical cell in the growing- 

 point of both stem and root. Ophioglossum is peculiar in that there is no 



pericycle in the stele of either stem or root ; 

 and in that, in some species (O. vulgatum, 

 lusitanicum, etc.) the stele of the root has 

 two xylem-bundles, but ouly one bast-bundle. 

 The collateral bundles of the stem of Bo- 

 trychium and Helminthostachys have rudi- 

 mentary cambium, which gives rise to a few 

 secondary xylem-tracheids ; these two genera 

 have also a formation of superficial cork on 

 the stem, and sometimes on the root. No- 

 thing is known as to the embryogeny of the 

 sporophyte. 



GAMETOPHYTE. The germination of the 

 spores has not been observed, but the mature 

 prothallium has been described in the case 

 of Ophioglossum pedunculosum and Botrych- 

 ium Lunaria. In both cases it is tuberous, 

 subterranean, destitute of chlorophyll, mo- 

 noecious ; the antheridia are sunk in the 

 tissue, and the short necks of the archegonia 

 project but little. It appears that the pro- 

 thallium is saprophytic, though possibly it 

 may possess chlorophyll in the early stages 

 of its development. It is altogether uu- 

 differentiated in Botrychium, being a some- 

 what ovoid body not more than half a line 

 long, with long scattered root-hairs, bearing 

 the antheridia chiefly on its upper surface, 

 the archegonia chiefly on the lower. In 

 Ophioglossum pedunculosum it appears to be 

 differentiated into a vegetative and a repro- 

 ductive portion; it consists, at first, of a 

 small round tuber from which springs a 

 cylindrical shoot which grows upward to the 

 surface of the soil. When the shoot reaches 

 the surface it ceases to elongate and becomes 

 lobed, assuming a green colour; it bears 

 antheridia and archegonia, and is therefore 

 (/) a gametophore, as distinguished from the 



original tuber which bears no sexual organs. 



Ophioglossum vulgatum (the Adder's tongue) is the British species of this 

 genus ; 0. lusitanicum has, however, been found in Guernsey. The epiphytic 

 species are 0. pendulum and 0. palmatum, both tropical forms ; the latter has 



FIG. 255. Botrychium Lunaria 

 (nat. size): w roots; st stem; bs 

 leaf-stalk ; x point where the leaf 

 branches; ,the sterile lamina (b) 

 separating from the fertile branch 



