116 THE OPHIOGLOSSALES 



be recognized in the young sporangium by cells arranged very much as they are in 

 the sporangium of Ophioglossum. The stalk is traversed by a short vascular bundle 

 which can first be recognized when the sporogenous cells are pretty well advanced 

 in their development. 



The sporangia of Helmtnthostachys on the whole more resemble those of 

 Botrychium than those of Ophioglossum. In the very young sporangiophore there 

 is developed a band of tissue on either side much like that in Ophioglossum (see 

 Bower 9, page 455)- Transverse sections of the fertile spike show that the spo- 

 rangiophores originate from certain groups of cells of this sporangiogenic band. 

 These young sporangiophores, however, project above the surface and later form 

 crowded projections which may undergo a greater or less degree of branching, so 

 that the number of sporangia borne upon a single one of these secondary sporangio- 

 phores may be considerable. These sporangiophores become irregularly lobed and 

 the final divisions of these develop into the sporangia in a manner which is very 

 similar indeed to that o^ Botrychium, but the individual sporangia are usually less 

 distinct. Bower's account of the further development may be quoted as follows: 



"It has already been noted that the position and number of the sporangia 

 which they bear are inconstant. In early stages it is impossible to distinguish 

 the cells which will give rise to the sporangia, but from rather older stages it ap- 

 pears that the sporogenous groups, together with the superficial cells which cover 

 them are referable in origin to the segmentation of a single superficial cell. More- 

 over, the first periclinal division of the cells defines the whole of the sporogenous 

 tissue from the protective wall. As the sporangia grow older they project from 

 the surface of the sporangiophore. The sporogenous mass increases rapidly in 

 bulk, while the cells surrounding the sporogenous mass to the extent of several 

 layers assume the character of a tapetum which gradually becomes disorganized; 

 finally the sporogenous cells separate and divide into tetrads. As the sporangia 

 approach maturity the upper part of the sporangiophore may grow out into an 

 irregular rosette of laciniae of vegetative tissue." 



A study of the older sporangia of Helmtnthostachys shows that the tapetum is 

 extraordinarily developed, constituting a very thick layer surrounding the mass of 

 spores (fig. 86). The clusters of fully developed sporangia are often very regular 

 in form (fig. 86, J), and remotely suggest the synangium of a Marattiaceous fern. 



