Pteridophytes Ophioglossales 



231 



a study of the development of sporangia, cut off the fertile portion 

 and fix it separately, using Flemming's weaker solution and staining 

 in iron-haematoxylin. The reduction divisions in the spore mother 

 cell take place after the leaves arrive above the surface. The vascu- 

 lar system of the sporangium-bearing portion and its relation to the 

 rest of the leaf is best shown by a series of thick (about 15 to 20 ju) 

 transverse sections mounted on a 5 XT-inch photographic plate. 



FIG. 76.Botrychium virginianum: photomicrograph of transverse section of root, 

 showing exarch protostele and radial arrangement of xylem and phloem. X23. 



They may be covered by a 5 XT-inch film, by a thin piece of mica, 

 or by any thin piece of glass. Of course, cover-glasses of this size 

 are made, but are not always available. 



The gametophyte.- -The gametophyte of Botrychium is subter- 

 ranean and tuberous. It sometimes reaches a length of 7 to 12 mm. 

 and a thickness of 4 to 5 mm. Usually, it is not more than 5 or 6 mm. 

 long and 2 or 3 mm. thick. Gametophytes showing the develop- 

 ment of antheridia and archegonia are not likely to be more than 2 or 



