VII PTERIDOPHYTA—FILICINE^—OPHIOGLOSSACEM 239 



granular matter. In these cells is found an endophytic fungus, 

 which probably acts as a mycorhiza. Multicellular hairs are 

 found growing from the upper surface of the prothallium. 



The growth of the prothallium is distinctly apical, and a 

 single definite apical cell seemed to be present, although it is 

 possible that there may be more than one initial. 



The infection of the thallus by the mycorhizal fungus is 

 chiefly through the short rhizoids upon the inferior surface of 

 the thallus. Jeffrey concludes that the affinities of the fungus 

 are with the genera Pythium or Completoria. 



Fig. 127. — Botrychium Virginianum. A, B, Germinating spore, X6oo: C, pro- 

 thallium ipr), with young sporophyte attached, X2; D, longitudinal section of the 

 prothallium, showing the foot of the embryo (.F), X4; E, first (?) leaf of a 

 young sporophyte, X2. 



As the prothallium grows older — it may evidently live for 

 several years — it becomes irregular in outline. It may finally 

 reach a length of twenty millimetres, and occasionally shows in- 

 dications of a dichotomy of the apex. 



Sex-Organs 

 The first antheridia form a small group upon the upper sur- 

 face of the prothallium while it is still very young. The later 

 ones form only upon the median ridge already referred to. 



