SUMMARY 491 



The roots appear early : the first root (sometimes precocious and 

 inordinately developed in accordance with the mycorhizic habit) is 

 essentially lateral upon the slowly developing axis, and the indefiniteness 

 of its position, above or below the basal wall, indicates its accessory 

 character. The whole shoot is, in fact, a rooted strobilus, which remains 

 usually simple ; but its strobiloid character is disguised by the abbreviation 

 of the axis, and by the slow succession and relatively large size of its 

 leaves. 



The first leaf of an adventitious bud of O. vulgatum, or the third leaf 

 in the sexually produced plant, may be fertile : in Botrychium Lunaria 

 the ninth leaf has been seen to be fertile. Such data, limited as they 

 are, show a record of early appearance of spore-producing members 

 unequalled elsewhere. They indicate a high probability that all the 

 leaves are of the nature of sporophylls, while abortion of the spike, so 

 frequently seen in various degrees in later leaves, would account for its 

 absence in those first formed. These may be expanded above ground 

 (HelminthostachyS) O. pedunculosum, B. virginianuw\ or may be arrested, 

 and appear as mere scale-leaves. The latter is clearly a consequence of 

 the underground and saprophytic habit of the prothallus, which diminishes 

 the necessity of early self-nutrition of the sporophyte, and thus leads to 

 reduction of the first leaves of the shoot as a purely secondary condition. 



On the other hand, the underground habit leads, as already explained, 

 towards a monophyllous development, with enlargement of the individual 

 leaf. This is imperfectly realised in the smaller species of Ophioglossum^ 

 which on our hypothesis would be the more primitive; but it appears 

 typically, though not universally, in the larger-leaved forms. Comparison 

 combined with biological reasoning indicates, then, that leaf-enlargement 

 has taken place. The anatomical facts accord with this : the solid or 

 slightly medullated xylem of the stock widens out upwards into a funnel 

 or cylinder, with foliar lacunae, where the single leaf trace-strands pass 

 out : the dilating of the stele follows the increase in size of the leaves in 

 the individual : this may be held to prefigure that of the race. Probably 

 the original foliar supply was here, as in the strobiloid forms, a single 

 strand, and this is still represented by the single bundle of the leaf- 

 trace. In O. Bergianum the single strand may be seen continued without 

 branching some distance upwards into the leaf. The branchings which 

 appear in other species early in its course may on our theory have 

 followed upon the enlargement and elaboration of the leaf. The Ophio- 

 glossaceae are phyllosiphonic from the first : but the case of Tmesipteris 

 has been adduced as showing that a transition may occur from the 

 cladosiphonic to the phyllosiphonic type : this may occur in any case 

 where the balance between the axis and the appendage is disturbed, so 

 as to increase the preponderance of the leaf. On our hypothesis of a 

 strobiloid origin for the Ophioglossaceae this has been the result of the 

 stunted development of the axis consequent on the subterranean habit, 



