FILICINEM. 



411 



of which is subsequently developed a cylindrical vermiform shoot, which grows 

 erect underground, is rarely and slightly branched, and elongates by means of 

 a single apical cell. When the apex appears above ground and becomes green, 

 it forms lobes and ceases to grow. The tissue of this prothallium is differen- 

 tiated into an axial bundle of elongated, and a cortex of shorter parenchymatous 

 cells, and the surface is clothed with root-hairs. With a transverse diameter 

 of \ to i\ Hues, it attains a length of from 2 lines to 2 inches. The pro- 

 thallium of Botrychium Lunaria is, according to Hofmeister, an ovoid mass of 

 firm cellular tissue, the greatest diameter of which does not exceed \ line, and 

 is often much less (Fig. 287, A\ It is light brown externally, yellowish white 

 internally, and provided on all sides with sparse moderately long root-hairs. 

 These prothallia are monoecious; each one produces a number of antheridia and 

 archegonia, which are distributed with tolerable uniformity over the whole of its 

 upper surface, with the exception, in O. pedunculosum, of the small primary tuber ; 

 in Botrychium it is the upper side which chiefly bears antheridia. 



The Antheridia are cavities in the tissue of the prothallium covered externally 

 by a few layers of cells, and in Ophioglossum only slightly projecting beyond the 



Fig. iZ-j.—Roirychittm Lunaria ; A longitudinal section of protballium (X 5°). c-c an archegonium, an an antheri- 

 diuui, w root hairs; B longitudinal section of the lower part of a young plant dug up in September (Xao) ; st stem, 

 b b' b'' leaves (after Hofmeister). 



surface. In this genus the mother-cells of the antherozoids originate by repeated 

 divisions from one or two cells of the inner tissue (covered externally by one or 

 two layers of cells) ; they form a mass of tissue of roundish form, and, as in 

 Botrychium, give rise to the antherozoids, which are similar in form to those of the 

 Polypodiacege, but larger ; they escape through a narrow opening in the cover of the 

 antheridium. 



The Archegonia are apparently developed in a similar manner to those of other 

 Vascular Cryptogams. Mettenius saw in Ophioglossum instances in which they 

 consisted of two cells, a superficial cell and one lying below it; this latter, he 

 considered, became the central cell, the former producing the neck of the arche- 

 gonium by dividing into four cells arranged crosswise, which then produce, by 

 further divisions, four vertical rows each consisting of two or more cells, and thus 

 form the neck. The wall of the ventral part which surrounds the central cell 

 is formed by divisions of the cells of the prothallium which surround it; the 

 ventral part is therefore completely imbedded, and only the neck, which is usually 

 very short, projects above the surface. Mettenius asserts that in Ophioglossum a 



