1891.] Morphology of Spore-producing Members. 269 



it grows older, the archesporial band becomes differentiated into 

 (a) sporogenous masses, which soon are densely filled with protoplasm, 

 and develop further into spores, as already known, and (&) sterile 

 tissues, which intervene between these, and develop into the septa 

 between the sporangia, together with part of the tapetnm. 



A similar continuous band of hypodermal tissue has been found in 

 Ophioglossum also, and is believed to be the continuous potential 

 archesporium. 



If the tissue thus recognised in Ophioderma, and, with less certainty, 

 in Ophioglossum, be the potential archesporium, and correspond to the 

 curved band of archesporium in Lycopodium, then the whole " fertile 

 frond "of Ophioglossum and Ophioderma must be homologous with 

 the sporangium of Lycopodium : the central tissue of the "fertile 

 frond" will be the counterpart of the sub -archesporial mass of 

 Lycopodium, and the whole will illustrate the result of elaboration, 

 partial sterilisation, and consequent partitioning of the sporangium. 



But it will further be pointed out that the Ophioglossacese, which 

 are a natural family with obviously close affinities, illustrate the pro- 

 gress of elaboration of the sporangium by still further steps within 

 their own circle of affinity. This will appear on comparison of 

 Helminthostachys, of which I have received well-preserved specimens, 

 collected in Ceylon, by Mr. J. Bretland Farmer. Here the " fertile 

 frond " is not so simple as in Ophioglossum; its homology is, however, 

 demonstrated by its position, and by the fact that its main features of 

 early development are similar. The spore-producing parts are borne 

 along the two lateral margins ; but, instead of the large sporangia 

 deeply sunk in the tissue, as in Ophioglossum, their place is taken in Hel- 

 minthostachys by branched outgrowths, each of which may bear a num. 

 ber of smaller sporangia ; these branched outgrowths may be styled 

 provisionally the sporangiophores. They are not disposed with strict 

 regularity, but are restricted to the margins of the " fertile frond," 

 and thus topographically they replace the sporangia of Ophioglossum : 

 functionally they do the same, for part at least of their tissue becomes 

 sporogenous. The development of them has been traced, but it need 

 not now be described in detail ; it will suffice to make the general 

 statement that it shows nothing incompatible with the theory above 

 put forward. The sporangia correspond in their development and 

 main features to those of Botrychium. A comparison of Helmintho- 

 stachys with Ophioglossum would point to the conclusion that in the 

 former is seen a further phase of elaboration, partial sterilisation, and 

 partitioning. If the archesporium of Ophioglossum were further sub- 

 divided by sterilised partitions, and the several parts raised by vege- 

 tative outgrowth of tissue, so as to project beyond the general 

 surface, the result would be something like that which is actually 

 seen in Helminthostachys. 



