COMPARATIVE DISCUSSION 479 



among themselves and not giving undue weight to the species which 

 happen to be the commonest leads almost inevitably to their seriation 

 in the way indicated above (pp. 431-446). The upright radial, unbranched 

 shoot is the central type, and the only departure from it is in the 

 large-leaved Helininthostachys, where the dorsiventral rhizome may be held 

 as illustrating a secondary condition ; the primitive stock was probably 

 upright and radial for them nil. It was also polyphyllous, as in most 

 other Vascular Plants, while each leaf bore the characteristic spike, which 

 is essentially identical in them all, whatever its actual nature may be 

 held to be. Within the family it is probable that the three genera 

 illustrate three distinct lines of descent from some common source, already 

 provided with a body of the nature of the spike. In Ophiog!<<ssitin the 

 original polyphyllous state is still seen in various smaller species : and it 

 is worthy of remark that the nearest similarity to other strobiloid types is 

 seen in those species in which the appendages are simplest and smallest. 

 But, as pointed out above, the monophyllous habit has biological advan- 

 tages in plants with an underground stock, and with its adoption followed 

 enlargement of the individual leaf, and of the spike, the two parts showing 

 some degree of parallelism of dimensions. Thus the ordinary type of 

 O. vit/gatnin is attained. Fission or chorisis of the spike is an occasional 

 occurrence in O. vulgatnm and other species, but it became a fixed 

 character in O. palniatiiin. It appears probable, however, that it is only 

 attained in this species in fully matured plants : thus the individual of 

 this species may be held to illustrate in its own life the origin of its 

 more complex form. Here again a parallelism exists between the irregular 

 lobing of the sterile lamina and the number of spikes which it bears. It 

 would be difficult to explain these characters in any other way than as an 

 ascending series involving chorisis. A probable line of reduction does, 

 however, occur : it is illustrated by the series O. pendulum, intermedium, 

 and simplex, the latter having no functional representative of the fertile 

 lamina. 



A distinct line, also of progression, is seen in Botrvchiiun, but with 

 different details. The series of forms seen in B. simplex (Fig. 240), and 

 in the young plants of B. Lnnaria, link on by their simplest forms with 

 the condition of a small Ophioglossum with simple sterile lamina and 

 unbranched spike : by very gentle gradations they lead on to the branched 

 sterile lamina and fertile spike characteristic of the genus, the branching 

 of the spike being closely connected with the enlargement and fission of 

 the sporangia. There is reason to believe, as Luerssen has indicated, 1 

 that these forms illustrate progress in the life of the individual, from the 

 simpler to the more complex : and the suggestion lies near to hand that 

 the individual in this respect "climbs up its own evolutionary tree." The 

 continuation of this method of advance would lead onwards to the most 

 complex forms, the spike and lamina preserving a parallelism as before. 



'Rah. Kryfi. Flora, iii., p. 579. 



