^lO 



MUSCINEM. 



becomes differentiated from the inner tissue which is to form the spores and elaters. 

 In FruUania it is a single circular disc of cells lying transversely beneath the dome 

 of the young sporogonium from which the vertical elaters, and by further divisions, 

 the mother-cells of the spores arise, a process which reminds one of what occurs in 

 Sphagnum. In most true Jungermannieae there is, on the other hand, a column of tissue 

 consisting of vertical rows of cells (surrounded by the wall of the sporogonium consisting 

 of two layers), out of which the elaters and spores are formed. The elaters lie, in 

 this case, horizontally, and radiate from the ideal longitudinal axis to the wall of the 

 sporogonium (Fig. 225). In Pellia the inner fertile tissue forms, after the diff'eren- 



FlG. 225 —yHn$:ey»iannia bicuspidata; longitudinal section of the unripe sporogonium sg, surrounded by the calyptra 

 ar; ar' archegonia which have remained unfertilised ; / base of the perianth ; st stem ; b leaf (after Hofmeister). 



tiation of the wall of the sporogonium, a hemisphere, from the cells of which arise the 

 spores and the elaters radiating from below upwards, in a similar manner to what 

 occurs in the Marchantieae. 



By a rapid extension of the hitherto short pedicel, the calyptra is ruptured at the 

 apex, and the globular sporogonium with the already ripe spores is raised up on it. 

 Even while the spores are ripening, the inner layer of the wall of the sporogonium is 

 absorbed; the single layer which still remains is ruptured at the apex, and splits into 

 four (rarely more) longitudinal valves, which, flying asunder in the form of a star, carry 

 with them at the same time the elaters, by which the spores are dispersed. The elaters, 

 when mature, are long fusiform thin-walled cells, round the interior of which run from 

 one to three brown spiral bands. 



