XIX] 



GAMETOPHYTE 



75 



parison of their fertile spikes. The simplest type as regards form is Ophio- 

 glosstim, with its two series of sunken sporangia. In H elniinthostacJiys the 

 external form as well as the development may suggest that the sunken 

 sporangia of Ophioglosswn are here replaced by the sporangiophores, with 

 their separate and smaller sporangia. In Botrychiujii the spike itself is 

 habitually branched, while the numerous separate and smaller sporangia 

 continue to hold the same relative position as in the unbranched spikes of 

 Ophioglossiim. As in almost all organic sequences, we might regard this 

 series either as an upward one of progressive elaboration or as a downward 

 one of reduction, or thirdly, as marking a divergence from some central 

 point. A decision on this point will have a special bearing on the probable 

 phyletic relations of the family. But this will not be discussed till after the 

 gametophyte generation and the embryology have been examined, and 

 meanwhile opinion must be held in suspense. (See p. 87.) 



The Gametophyte. 



The prothallus in all of the Ophioglossaceae is saprophytic, and it grows 

 normally as a mycorhizic, colourless body underground. Campbell {Eusp. 

 Ferns, p. 6) has traced the germination in several distinct instances, and 

 found that after the first few cell-divisions in the germinating spores growth 

 stops, unless there is infection by the mycorhizic fungus. This appears to 

 give the necessary stimulus, and thereafter development proceeds. Chloro- 

 phyll in small quantity has been seen in some early stages, but not in all. 

 Mettenius stated for Ophioglossiim pedunculosuvi that chlorophyll may be 

 developed if the prothallus appears above ground, and Bruchmann also 

 found this for Ophioglossiim vulgatiim. But for all practical purposes the 

 gametophyte of the Ophioglossaceae is saprophytic. 



The adult prothallus of Botrychium virginianum (Fig. 375) grows about 



Fig. 375. Prothallus of Bolrychiwn virginiatium (after Campbell). A, B, germin- 

 ating spore; C, three gametophytes, fw = embryo (X3); D, section of game- 

 tophyte ( X 9) : the shaded region is that occupied by the endophyte; c? , 

 antheridia; E, apical region of gametophyte (x 120); F, short multicellular 

 hair, or paraphysis. 



