308 HOFMEISTER, ON 



of a semi-transparent substance, which is not rendered 

 blue by iodine. On the side turned towards the surface 

 of the earth the prothallium mostly produces antheridia, 

 and on the opposite side archegonia. The former have the 

 appearance of cavities in the mass of the prothallium, which 

 open outwards with a very narrow mouth (PI. XLI, figs. 

 5, 6, 10 6 .) The spermatozoa are hardly distinguishable 

 from those of the Polypodiacese, except in being half as 

 large again as the latter. The walls of empty antheridia are 

 coloured light brown, and are covered with a granular sub- 

 stance. The archegonia (PI. XLI, figs. 5, 10*), are en- 

 tirely buried in the prothallium, but agree in other respects 

 with those of the ferns. Spores sown artificially swelled to 

 twice their natural size, but underwent no further change. 

 The membrane of a spore thus swollen was found attached 

 to a prothallium, and was recognisable by the three promi- 

 nent ridges of the outer surface, which meet at angles of 

 120 (PL XLI, fig. 7). 



The position of the embryo with regard to the prothal- 

 lium differs widely from what occurs in the Polypodiaceae 

 and Rhizocarpese. JBotrychium in this respect is allied to 

 those vascular cryptogams, whose prothallium, like that of 

 the Ophioglosseae, is devoid of chlorophyll (Isoetes, Selagi- 

 nella). The punctum vegetationis of the embryo lies near 

 the apex of the central cell of the archegonium. The first 

 roots originate underneath it near the base of the archego- 

 nium (PI. XLI, fig. 6*; PI. XL1I, fig. l b ). In con- 

 sequence of the downward direction of the mouth of the 

 archegonia, the embryo has to turn half round in order to 

 give its bud an upward direction, so that the prothallium 

 is found attached to it laterally. The youngest germ- 

 plants found attached to prothallia, exhibited at least 

 two roots, and also near the punctum vegetationis, a more 

 or less developed hemispherical or oval knob (PI. XLI, figs. 

 8 10). The outside of the latter (on account of the 

 colour) bears only a distant resemblance to the roots : its 

 internal structure differs widely from theirs : the hemi- 

 spherical body consists of wide parenchymatal cells, which 

 become gradually smaller and flatter towards the outer 

 surface : a rudimentary vascular bundle consisting, with 



