THE HIGHER CRYPTOGAMIA. 159 



the origin of the Vaginula, the formation of which commences 

 in Phascum and Bryum at a very early period, at the 

 time when the fruit-rudiment only occupies the upper two- 

 third parts of the archegonium (PL XX, fig. 15 ; PL XXI, 

 fig. 4; PL XXIII, fig. 3). In Sphagnum the vigorous in- 

 tercalary multiplication of the cells of the end of the 

 stem which bears the archegonia begins at a much 

 earlier period : even before the young archegonium has 

 attained its full number of cells. The very short fructify- 

 ing side-shoots of Sphagnum cymbifolium and S. squarrosum 

 usually develope one, at the most two archegonia, with 

 a remarkably fully developed ventral portion, and a strongly 

 clavate apex. When the latter is about to burst the 

 number of the cells of the end of the stem which bears 

 the archegonia (and which in Sphagnum is conical) in- 

 creases, without any change occurring in the circumference 

 of the conical mass of tissue. Its upper surface bears rudi- 

 mentary leaves destined to develope themselves in the fol- 

 lowing summer, at the commencement of the ripening of 

 the fruit (PL XVIII, fig. 15). 



By the continuous longitudinal growth of the fruit- 

 rudiment its lower end is pressed continually deeper into 

 the tissue of the lower part of the archegonium, until at 

 last it reaches the parenchyma of the vaginula, to the 

 base of which it penetrates. The pressure is caused by 

 the resistance which the arcuate portion of the archego- 

 nium underneath its neck exerts upon the apex of the 

 fruit-rudiment. The tissue of the stem itself resists the 

 further penetration of the lower end of the fruit-rudiment. 

 The ventral portion of the impregnated archegonium 

 which has become the calyptra, now usually assumes the 

 shape of a bell, in consequence, it would seem, solely of 

 the expansion of its cells (Phascum, PL XXI, fig. 24, 

 Gymnostonium, Eucalypta, Orthotrichum). The cells of 

 its inner tissue become dissolved, only the single layer of 

 the outer surface remaining (PL XXI, fig. 4). The hollow 

 cavity between the latter, and the fusiform fruit-rudiment, 

 is filled with watery fluid. The increased tension of the 

 side walls of the calyptra, which is produced by the 

 sudden and considerable expansion of the median cells of 



