THE ADULT SPOROPHYTE 109 



secondary modifications of an originally sterile leaf. At present it is the belief of 

 most students of the ferns that the fertile structures of the sporophyll are older than 

 the sterile ones, and this has led to a quite different interpretation of the real nature 

 of the fertile segments. 



Bower (Bower 9) has treated at length the different theories that have been 

 proposed to explain the nature of the fertile spike in the Ophioglossaceae. We can 

 only refer briefly to some of the more important of these. Mettenius (Mettenius 1) 

 considered that the two parts of the leaf were of equal value, but he gives no data 

 as to their origin. Later writers, e. g., Holle (Holle 1), Goebel (Goebel 1), and very 

 recently Chrysler (Chrysler 1), consider the fertile spike to be the equivalent of the 

 fertile pinnae of such a fern as Aneimia. Holle and Chrysler think that the single 

 median spike is the equivalent of two united pinna?. Goebel thinks that the spike 

 represents a single pinna which has arisen in a median position instead of upon 

 the margin. Chrysler's results are based mainly upon a study of the distribution of 

 the vascular bundles in Botrychium. His results, however, do not take into account 

 the early development of the sporangiophore and its relation to the primordium 

 of the very young fertile leaf. 



Bower, who has made the most complete study of the development of the spore- 

 bearing parts in the Ophioglossaceae that has yet been published, concluded in his 

 earlier work that the spike of Ophioglossum is morphologically equivalent to the 

 single sporangium of Lycopodium. In this view he was supported by Strasburger 

 and Celakovsky (Celakovsky 1). More recently, however, he has modified his view 

 (Bower 9) and concludes that the sporangial spike is a distinct organ, for which he 

 suggests the name "sporangiophore." This later interpretation we believe to be 

 the correct one. 



In Ophioglossum the sporangiophore develops a peduncle which is often very 

 much longer than the sterile portion of the leaf and forms much the most conspicuous 

 portion of the sporophyll (fig. 55). The fertile portion of the sporangiophore is a 

 flattened spike along whose margins the two rows of large sporangia are borne. 

 These project very little, the cavity of the sporangium being deeply sunk in the tissue 

 of the spike and covered by several layers of cells forming the outer wall of the spor- 

 angium. The number of the sporangia in a spike may be only six or seven in some 

 of the small forms of Euophioglossum, or it may be very large, as it is in the great 

 spikes of O. pendulum. 



In O. pendulum and O. intermedium the spike is more flattened than it is in the 

 species of Euophioglossum and the central sterile portion is wider in proportion. 

 Stomata are almost entirely absent from the epidermis of the spike in O. pendulum, 

 although occasionally a few are found in the central region. In 0. intermedium 

 they are more numerous than in 0. pendulum, but much less abundant than in the 

 species of Euophioglossum. In the latter they may occur even upon the epidermis 

 of the wall of the sporangium. The most marked exception in the position of the 

 sporangiophore is seen in the section Cheiroglossa (plate 5). In this form there are 

 several sporangiophores developed upon the leaf. Although these are apparently mar- 

 ginal in position, it is claimed by Bower that they are really always developed upon 

 the adaxial surface of the leaf. Some of the smaller forms may show a single spike 

 which occupies a central position, very much like that of 0. pendulum (plate 5, 3). 



In some of the simpler forms of Botrychium simplex the sporangiophore is very 

 much like that of a small Ophioglossum, except that the individual sporangia are 

 more distinct, although the base of the sporangium is coherent with the margin of 

 the sporangial spike. In all of the other species of Botrychium, however, the spor- 

 angiophore branches, the degree of branching following very closely that of the 



