io8 MOSSES AND FERNS chap. 



forms 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. Here 

 the germinating spore divides by a transverse wall into two 

 equal cells, one of which continues to grow and divide until a 

 short filament is formed. After a varying number of transverse 

 divisions an oblique wall is formed in the terminal cell, and a 

 second one nearly at right angles to it. By these divisions the 

 dorsiventral character is established, the first-formed segment 

 being ventral. A third oblique wall now arises, intersecting 

 both of the others, and the three include a tetrahedral cell 

 which is the permanent apical cell of the young plant. The 

 ventral segments do not at first form any trace of leaf-like 

 structures, and in the dorsal segments the leaves are at first 

 simple rows of cells ; but a little later the leaves show plainly 

 their two-lobed character, each being made up of two rows of 

 cells united at the base. From the ventral segments the 

 amphigastria develop gradually, being quite absent in the 

 earlier ones. ChiloscypJius closely resembles Lophocolea, but the 

 filamentous protonema is longer, and is often branched. A 

 similar filamentous protonema is present in Cephalozia {^Jungev- 

 inannid) bicuspidata and other species. 



Lejeunia ^ shows a most striking resemblance in its early 

 stages to the simple thalloid Jungermanniacese. The germinat- 

 ing spore forms either a short filament or a cell surface (Fig. 

 5 I, A). In either case, at a very early stage, a two-sided apical 

 cell is established, and for a time the young plant has all the 

 appearance of a young Metzgeria or Amur a. This two-sided 

 apical cell gives place to the three-sided one found in the older 

 gametophyte, and the leaves and stem are gradually developed 

 as in Lophocolea. 



In Radula'," and according to Goebel, much the same con- 

 dition occurs in Porella, the first divisions of the spore give rise 



^ Goebel (12). - Goebel (12) ; Hofmeister (i), p. 55. 



