X THE HOMOSPOROUS LEPTOSPORANGIATJE 359 



both sides of the lamina. The development of the stem offers 

 no peculiarities. The apical cell is of the tetrahedral form 

 found in the mature sporophyte. 



The root is bulky, and the apical cell relatively small, with 

 large segments, dividing less regularly than in Onoclea, and on 

 the whole approaches most nearly to Botrychiiun. The form 

 of the apical cell is like that of Onoclea or Botrychium, and is 

 interesting because in the later roots this is replaced by another 

 type, so that this would indicate that the three-sided form 

 found in so many cases is the primitive condition. The vas- 

 cular bundle is diarch. 



The foot is very large, and while formed originally from 

 the upper hypobasal quadrant, it encroaches more or less upon 

 all the others. Very early its 

 cells cease to show any regular 

 order in their divisions, and di- 

 vide more slowly than the other 

 cells of the embryo, so that they 

 become decidedly larger. The 

 cells lose much of their proto- 

 plasm as they increase in size, 

 and serve simply as absorbent 

 organs. They are in close con- 

 tact with the prothallial cells, 

 and crowd upon them until the ^^^^ ^o^.-Young sporophyte of o. 



foot penetrates deep into the Claytoniana, still attached to the 



,1 11- 1 11 -i prothallium, X6. 



prothallium, whose cells it par- 

 tially destroys. It Is upon the large development of the foot, 

 whose outer cells are sometimes extended into root-like exten- 

 sions like those in Anthoceros, that the young embryo is main- 

 tained so long at the expense of the prothallium. 



Frequently more than one embryo begins to develop, and 

 sometimes a number of archegonia may be fertilised; but no 

 cases were met with where more than one embryo came to 

 maturity, although it Is quite possible that this may occur. 



In all the Osmundacese the mature stem Is a stout rhizome, 

 which In the genus Todea may form an upright caudex, a metre 

 or so In height. The bases of the stipes are broadly winged 

 and these sheathing leaf-bases persist for many years, com- 

 pletely covering the surface of the stem. According to Faull 

 (i)^ who has made a very thorough study of the anatomy of 



