THE HIGHER CRYPTOGAMIA. 41 



ripe, renders the boundary lines of the four or five eells of 

 which the spore is composed very indistinct. 



Under cultivation, irregularities in the development of 

 the spores of Pellia are rather frequent. The primary 

 halves of young spores sometimes divide by longitudinal 

 septa instead of by transverse ones (PL V, fig. 25). Not 

 unfrequently all the mother-cells of a fruit become abortive 

 shortly before the period of the independent existence of 

 the spores, excepting a few of the mother-cells, which in 

 such a case attain almost double the usual size. 



The vegetative development of the rest of the species 

 mentioned in the title of this chapter differs materially from 

 that of Pellia. The growth of Metzgeria furcata in length 

 and breadth is discussed by Nageli, in his essay on the 

 study of cell-multiplication, " Wachsthumsgeschichte der 

 Laub. und Lebermoose" (' Zeitschrift f. Botanik,' Heft 2). 

 My view of the process, as the following remarks will show, 

 differs in some subordinate points from that of Nageli. 



The longitudinal growth of the strap-shaped stem, which 

 is slightly rounded at the apex, results from the conti- 

 nually repeated formation of septa, spreading right and left, 

 and perpendicular to the surface of the stem (PL V, figs. 

 26, 27, 28). The cells of the second order thus produced, 

 whose basal outline is a rather long five-sided figure, 

 divide first by a septum at right angles to the side walls and 

 perpendicular to the surface of the stem. In the outer- 

 most one of the newly formed cells the same process is 

 repeated again : a septum appears parallel to the one last 

 formed, or else this cell, as well as its inner sister-cell, 

 divides by a longitudinal septum parallel to its side walls. 

 In the former case the shoot grows in breadth ; in the latter 

 in length. In both cases the division is repeated several 

 times, always in the outermost cells, by septa at right angles 

 to the side walls. The development of each shoot begins 

 with the second form of cell-multiplication of the cells of 

 the second order ; as the longitudinal growth draws to 

 a close, the shoot is prepared for furcate ramification 

 (PL V, fig. 28), and thus the first form of cell-multiplica- 

 tion steps in. In each of the masses of cells which are 

 formed by the division of a cell of the second order, septa 



