268 Prof. F. 0. Bower. Studies in the [Dec. 17, 



Selaginella, its sporangium appears to be comparable to the Selago 

 type of Lycopodium, though with differences of detail, which need 

 not now be specified. 



The results obtained by observation of the Lycopodinae have been 

 used for purposes of comparison with the Ophioglossaceae, and the 

 result is a view as to the real nature of the so-called "fertile frond." 

 This structure has long been a morphological crux, and various 

 opinions have been held with regard to it, which severally make 

 demands upon morphological faith. The theory now to be put forward 

 is, that the " fertile frond " is an elaborated and partitioned sporangium, 

 homologous with the smaller and non-partitioned sporangium of the 

 Lycopodinae. Developmental evidence will now be adduced in support 

 of this theory. 



The " fertile frond " of Ophioglossum vulgatum arises as an out- 

 growth of the upper surface of the " sterile leaf " : not, it is true, at 

 the base, but rather below the middle : the cell- divisions do not cor- 

 respond in detail to those in the young sporangium of Lycopodium, 

 but I do not think that, at the present day, this will be reckoned as a 

 material ground for rejecting an homology. There is in fact, at first, 

 a single initial cell, with rather irregular segmentation, but the apical 

 growth of the elongated and upward directed " fertile frond " passes 

 over shortly to the type with, apparently, four initials. 



The origin of the archesporium and sporogenous tissue has been 

 traced in Ophioderma pendulum by the help of material supplied 

 through the kindness of Dr. M. Treub. In this plant, as in Ophio- 

 glossum, the sporangia are deeply sunk in the " fertile frond," and 

 form a longitudinal series running along each lateral margin of it, 

 and extending to the extreme apex. Transverse sections in the 

 young state would thus show the archesporia at the most curved 

 points of the elliptical section. In the youngest transverse sections 

 which were observed, the archesporial tissue appears composed of 

 many cells, and it is doubtful whether all be referable to a single 

 parent cell ; but, seeing that this section would correspond to what is 

 seen in a radial or a transverse section of the sporangium of Lycopodium, 

 and that there is a difference (e.g., between L. selago and L. clavatum) 

 as to the reference of the archesporium to a single cell in such sections 

 in different species of that genus, this question cannot be considered 

 as a vital one. 



The archesporial tissue thus seen in transverse sections of the young 

 " fertile frond," is found in tangential and radial sections to be a con- 

 tinuous land, which extends along each margin to the apex ; it is 

 believed to correspond to the curved band of archesporial tissue in 

 Lycopodium, and may, therefore, be styled the potential archesporium. 

 But whereas in Lycopodium the whole of this tissue forms spores, 

 only parts of it develop as sporogenous tissue in Ophioderma : for, as 



