380 



VASCULAR CRYPTOGAMS. 



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 Ophio- 

 glossum a prolongation of the oosphere (probably a canal-cell, as in Ferns and 



Rhizocarps), penetrates into the lower part of 

 the neck. 



The Asexual Generation. The first divi- 

 sions of the oospore are not known; but the 

 mode of formation of the embryo differs, as 

 may be concluded from the circumstances al- 

 ready named, from that of Ferns. Mettenius 

 states that in Ophioglossum pedunculosum the end 

 of the embryo which faces the apex of the pro- 

 thallium developes into the first leaf, while the 

 opposite end produces the first root. Unlike 

 what occurs in Ferns, the concave upper side 

 of the first leaf faces the neck of the archego- 

 nium ; the rudiment of the stem (which Met- 

 tenius terms the 'primary rudiment of the em- 

 bryo '), lies nevertheless on the side of the 

 embryo which faces the base of the archego- 

 nium. Hofmeister, on the other hand, makes 

 the following statement with regard to Botry- 

 chium : — ' The position of the embryo with re- 

 spect to the prothallium differs widely from that 

 which occurs in the Polypodiaceae and Rhizo- 

 carpese ; Botrychium approaches in this respect 

 those Vascular Cryptogams the prothallium of 

 which, like that of Ophioglossaceae, is destitute 

 of chlorophyll (Isoetes, Selaginella). The piinc- 

 iinn vegetationis of the embryo lies near the 

 apical point of the central cell of the archego- 

 nium; the fi.rst roots arise beneath it, near the 

 base of the archegonium ' (/. c. p. 308). 



The processes of growth of the mature plant 

 have not yet been ascertained with as much cer- 

 tainty as in other Vascular Cryptogams. In 

 Ophioglossuni vulgatum and Botrychium Lunaria 

 the erect stem, buried deep in the earth and 

 growing very slowly in length, appears never to branch. Even the comparatively 

 thick roots rarely branch, and it is not known whether the branching is then 

 monopodial or dichotomous. The flattened apex of the stem, surrounded by the 

 insertions of the leaves, is buried deeply in the leaf-sheaths, and shows, in Ophioglos- 

 sum vulgatum, according to Hofmeister, a three-sided pyramidal apical cell as seen 

 from above. The leaves have a sheathing base, and each is completely enclosed in 



Fig. 283. — Longitudinal section through the 

 lower part of a mature plant of Botrychuem Lic- 

 naria. st stem, ^^' fibro-vascular bundles, iv a 

 young root, b apex of the stem, * b' h'' h"' the 

 four leaves already formed, b'" the one unfolded 

 during the present year : b' shows the first indi- 

 cation of the branching of the leaf; in b'' this has 

 advanced further ; m is the median line of the 

 sterile lamina, having already its lobes right and 

 left which are not shown ; y the fertile lamina with 

 the young ramifications, on vvliich the sporangia 

 will be produced (x about lo). 



