456 



OPHIOGLOSSALES 



(Fig. 255 A). There seems to be no fixed type of segmentation of the cells 

 which leads to the formation of these sporangiophores, and though, as 

 they increase in size, their apex may sometimes be occupied by a 

 wedge-shaped cell, more frequently no such cell can be found (Fig. 255 P-). 

 The subjacent tissue may sometimes increase to a slight degree below 

 a young sporangiophore, but it is obvious from the drawings, both of 

 transverse and of longitudinal sections, that the sporangiophores are 

 derived essentially from the superficial cells. Now this is also the case 

 with the sporangia of Ophioglossum, in which the sporangiogenic band is 



FIG. 255. 



Helminthostachys zeylantca, Hook. A early ; phases of sporangiophores. Note the 

 variability of size, shown also in the tangential section F. B and C = older sporangiophores. 

 C, D, and Gshow stages of development of the sporangium, with the sporogenous cells 

 shaded. X 200. 



in the first instance composed of superficial cells ; thus there appears to 

 be correspondence as regards the place of origin of the spore-producing 

 members of the two genera. 



Fig. 255 B illustrates the most regular type of these very variable organs; 

 already in the central part longitudinal divisions are taking place which 

 indicate the position of the central vascular bundle. The great differences 

 in size which they show when young are suggested by the tangential section 

 shown as Fig. 255 F. As they develop further the sporangiophores may 

 become irregularly lobed or branched. Thus, though disposed with some 

 regularity along the margins of the fertile spike, they are themselves very 

 variable in size, form, and mutual arrangement. 



It has already been noted also that the position and number of the 

 sporangia which they bear is inconstant. In early stages it is impossible 



