58 HOFMKISTKR, ON 



division of a single cell of the upper surface of the stem, 

 which protrudes in an arched form, at an early period, above 

 the bounding surface of the stem. One of these cases is 

 Fossombronia pusitta. Here the leaf, at its first appearance, 

 is exactly like a short hair ; the papilleeform protruding cell 

 of the upper surface of the stem is soon separated from the 

 original cavity of the cell by a transverse septum, and after- 

 wards divided by a septum parallel to the latter, into a 

 lower cylindrical, and an upper clavate cell. The fluid con- 

 tents of the latter are tolerably transparent, those of the 

 former exhibit numerous chlorophyll-granules (PI. IV, 

 fig. 25). The lower cell only, divides in rapid succession; 

 first by a transverse septum, and then the lower one 

 or both of the newly-formed cells, by a septum at right 

 angles to the last, and to the surface of the young leaf 

 (PL VI, fig. 27). The upper pair of cells of the third 

 order divide by transverse septa ; longitudinal septa appear 

 in the lower one, followed by transverse septa again in the 

 outer cells (PI. VI, fig. 26). The like succession of divisions 

 takes place in the lower of the two pairs of cells, which 

 originated in the transverse division of the two cells of the 

 third order adjoining the apical cell, and is repeated, (with - 

 the recurrence of the transverse division of the- upper of 

 these pairs of cells,) continually in the two newly-formed 

 cells lying nearer to the base of the leaf on the right and 

 left of the median line. In the mean tune, by frequent 

 longitudinal division of the marginal cells of the lower part, 

 the leaf increases considerably in breadth (PL VI, fig. 28) ; 

 the one longitudinal half is always more vigorous than the 

 other. This multiplication lasts much longer at the base 

 of the leaf, where it keeps pace with and ultimately exceeds 

 the growth of the stem, than it does at the upper margin, 

 towards which it gradually diminishes. Individual cells of 

 the margin continue to multiply for a longer period than 

 their neighbours, repeating in miniature, in the mode of 

 their multiplication, the formation of the leaf; in conse- 

 quence of this the leaf assumes its multi-angular shape. 



The rudimentary appendages of the leaves of the Lopho- 

 colese are, as has been already observed, short row r s of cells ; 

 the first rudiments of the leaves themselves are nothing 



