THE HIGHER CRYPTOGAMIA. 131 



The cell of the second degree is thus divided into an 

 upper daughter-cell, with three-sided fore and hind surfaces, 

 and an under, four-sided cell (PI. XVII, fig. 2). The free 

 outer wall of the former forthwith becomes arched outwards, 

 and is recognisable as the rudimentary cell of a leaf. The 

 latter (the lower cell) divides by means of longitudinal 

 septa, alternately tangential and radial to the axis of the 

 stem, which division continues until the completion of the 

 full number of the cells of the portion of the stem in 

 question. There is no very great regularity in the suc- 

 cession of these divisions. Sometimes one, sometimes the 

 other, occurs first ; frequently one step of the ordinary suc- 

 cession is passed over, and made good at a later period. In 

 every case, however, one phenomenon is constant — at a point 

 near the end (of the stem), about three cells downwards 

 from the apical cell, the number of the cells of the circum- 

 ference of the young stem is eight. An inequality in the 

 multiplication by radial longitudinal septa of the cells of 

 the third degree also occurs regularly ; one of these cells in 

 each zone of the stem must lag about one division behind 

 the two others. Por if this multiplication in the cells of 

 the third degree were uniformly active, it would follow that, 

 inasmuch as three cells of the third degree must occur in 

 each transverse section of the stem, the number of cells of 

 each girdle of the outer surface of the stem must be a 

 multiple of three. 



A transverse section of the perfect stem usually exhibits 

 a number of peripheral cells which is a multiple of eight. 



septa inclined alternately in only two opposite directions, I was led to believe 

 that I must necessarily assume the same to be the case in Sphagnum and Equi- 

 setum, where 1 observed the pointed apical cells of the stem-bud had the 

 appearance of being two - surfaced. The cases of three-sided apical cells 

 which came under my observation, and of which I have given figures in 

 pi. xix, fig. 7, of the 'Vergleichende Untersuchungen,' I considered to be 

 instances of a mode of growth which caused a change in the form of the 

 apical cell between the period of each two divisions. Later observations 

 have convinced me that Nageli's representation of the mode of increase of 

 the apical cell of the stem of Sphagnum, and Cramer's account of the similar 

 process in Equisetum, are correct. Erom this error there necessarily arose, 

 in the case of Sphagnum, an additional one, viz., in the account given of the 

 further division of the cells of the second degree, and in the statement that 

 the rudimentary cells of the leaves were derived from these latter cells, 

 which error I have corrected in the text above. 



