152 



MORPHOLOGY 



pbore development ran be traced from the subarchesporial pad of Lycopodiales 

 to the fertile spike of Ophioglossales, whose leaf would thus become a sporophyll. 

 This conception of the simple spike of Ophioglossum, with its sessile sporangia, 

 is difficult to apply to Helminthostachys with its stalked sporangia, and to Botry- 



chium with its more or less branching spike. Recent anatomical studies, however, 

 suggest that this " fertile spike " may have arisen by the fusion of lateral branches 



356 



Figs. .355-358. — Sporangia of Ophioglossum: 355, the band of sporogenous tissue 

 developing on one side of the fertile spike; 356, cross section of the sporogenous band; 

 357, 358, different stages in sterilization, breaking up the band into separate sporogenous 

 masses, each of which develops a sporangium. — After Bower. 



on opposite sides of the main axis. If this is the case, the relationship with the 

 Marattiaceae and other ferns is clear. It is interesting to note that the spike branches 

 as the leaf branches, being simple in the simple-leaved species of Ophioglossum 

 and branching in the compound-leaved species of Botrychium. 



Sporangium. — The development of the individual sporangium is of 

 the usual eusporangiate type, but the remarkable behavior of the tape- 

 turn deserves special mention. The walls of the tapetal cells break 

 down, and the protoplasts thus liberated unite to form a nutritive plas- 



