480 OPHIOGLOSSALES 



On this view the two genera, starting from a common source, would be 

 held to illustrate two distinct lines of progression to a more complex state. 



The third genus, with its single highly elaborate species, gives no such 

 suggestion of its origin by comparison of nearly allied species. It stands 

 as the most isolated member of the family : but its normal spike is 

 evidently similar in plan to that of a large Ophioglossum, supposing its 

 marginal rows of sunk sporangia were replaced in Helniinthostachys by 

 serried ranks of sporangiophores. There is a biological probability that 

 such an advance should occur in a large spike bearing many spores, for 

 thereby the advantage is gained of more ready nutrition of the subdivided 

 sacs, and more easy dissemination of the spores when mature. 



The progressive advance thus suggested for the Ophioglossaceae is in 

 accord with biological probability, in a series with a marked tendency to 

 a monophyllous state, and consequent enlargement of the individual leaf. 

 Provided the nutrition be available, an increase in numbers of spores is 

 an advantage in any homosporous form. But an indefinite increase in 

 size of individual sacs raises difficulties of nutrition : subdivision is thus 

 to be anticipated in any progressive series, and that is seen in Ophio- 

 glossum. A projecting position of the individual sporangium is an 

 advantage in dissemination of the spores. This is ill provided for in 

 Ophioglossum, and in this respect Botrychium and Helniinthostachys show 

 a more effective state. It appears to me difficult, without special reasons 

 assigned, to recognise this family as a series of reduction, for it would 

 be in opposition to these biological considerations. On the other hand, 

 comparisons within the family clearly indicate an upward rather than a 

 downward progression, while in any case those who hold a theory of 

 reduction would find peculiar difficulty in explaining the condition seen 

 in Ophioglossum palmatum. 



The next step will be to discuss the morphology of the fertile spike, 

 and to see what are its nearest correlatives among the members of other 

 Vascular Plants. The spike in all the representatives of the family is 

 clearly the same part : it is in fact truly homologous, or homogenous in 

 the strict evolutionary sense. This follows from the high degree of 

 constancy of position and function which it shows in normal cases. 



Various theoretical explanations of its morphological nature have been 

 given by different writers. It has been suggested by Braun 1 that the 

 sterile frond is a foliage leaf, and the fertile spike the only developed 

 leaf of a bud seated in its axil, and coalescent with it. Somewhat later, 

 Roeper (1843) published the opinion that the sterile spike and fertile leaf 

 are equivalent that is, borne by the same axis but coalescent together. 

 Subsequently he substituted for his old view the opinion that the fertile 

 spike is the result of coalescence of two lateral, lower, fertile pinnae of a 

 frond, of which the remainder is usually sterile. 2 Lastly, Goebel has put 

 forward the opinion that the fertile spike is the lowest pinna of the 



1 Flora, 1839, p. 301. * Bot. Zeit., 1859, p. 271. 



