THE HIGHER CRYPTOGAMIA. 63 



in the latter plant. Soon, however, a new process of 

 cell-formation appears at the side-edges of the leaf, under- 

 neath the place of origin of these teeth ; commencing by 

 a lateral expansion of one of the marginal cells, followed 

 by a cutting off, by means of a transverse septum, of the 

 protuberance thus formed, and by repeated transverse divi- 

 sion of the newly-formed cells. By this means the hitherto 

 double-pointed leaf becomes four-pointed. 



The leaves of Radula camplanata are developed in all 

 their parts in a manner precisely similar to that of the 

 superior leaves of Frullania dilated a (PI. XI, fig. 15). 

 In this species, also, the apical cell of the lower lobe 

 after its last division usually grows out into a clavate 

 hair (PI. XI, fig. 1). The multiplication of the cells of 

 the base of the leaf lasts for a considerable time after 

 the termination of the division of the apical cells. 



The arrangement of the cells in the leaves of the 

 round-leaved common Jungermannia? {J. curta, crenulata, 

 Alicularia scalar is) very much resembles the later condi- 

 tion of the upper lobe of the superior leaves of Frnlla- 

 nia ; it answers exactly to the arrangement of the cells 

 in the direction of the surface, of young shoots of Pellia 

 (PI. VII, fig. 21). 



The leaves of the Jungermanniae usually exhibit a very 

 decided inclination to development in breadth. I know 

 of no species in which a single apical cell divides by means 

 of septa spreading alternately right and left, and in which 

 the division lasts until the termination of the growth 

 of the leaf. The development of the leaves of all Jun- 

 germanniae agrees in this, that the leaf originates in the 

 extension outwards of one or more cells of the bounding 

 surface of the stem close underneath its growing apex, 

 and the subsequent separation by septa of the protuber- 

 ances thus formed from the original cell-cavity. This 

 first rudiment of the leaf grows at first exclusively by 

 division of the cells of its apex and edge. After a 

 series of such divisions, sometimes after very few (in ex- 

 treme cases, as in Fossombronia, and in Haplomitrium 

 according to Gottsche, after one single division) there en- 



