in 



I HE JUNGERMANNIALRS 



113 



perianth; but in others it may reach a length of several centi- 

 metres. 



The development of the perianth is quite independent of 

 fertilisation, and not infrequently it contains, although fully 

 developed, only abortive archegonia. It is not always formed, 

 but when present, according to Leitgeb, it is the product of the 

 older segments of the apical cell from which archegonia are 

 formed, and arises as a sort of wall about the whole group of 

 archegonia. In Porella, as well as most of the foliose He- 

 paticae, the capsule opens by four equal valves, the lines of 

 splitting corresponding, according to Leitgeb, to the first 

 quadrant walls in the young embryo. 



The germination of the spores shows a great deal of varia- 

 tion, and has been studied in a large number of forms by 

 several observers. Recently a number of tropical species have 



Fig. 58. — Frullania dilatata. Development of the embryo, X300 (after Leitgeb); x, x, 

 the archesporial cells. The numbers indicate the primary transverse divisions. 



been investigated, especially by Spruce (2) and Goebel (12), 

 and some extremely interesting variations have been discov- 

 ered. In these forms and when the exospore is not strongly 

 developed, it is simply stretched by the expanding endospore, 

 and finally becomes no longer discernible ; but when it is clearly 

 differentiated, it splits with the swelling of the endospore and 

 then remains unchanged at the base of the young plant. The 

 germinating spore may give rise to a cell mass immediately, 

 which develops insensibly into the leafy axis, or it may form a 

 simple or branched protonema of very different form, which 

 sometimes reaches a large size and upon which the leafy axis 

 arises as a bud. 



The simplest form may be illustrated by Lophocolea, in 

 which the germinating spore divides by a transverse wall into 



two equal cells, one of which continues to grow and divide 

 8 



