THE HIGHER CRYPTOGAMIA. 137 



be drawn from the position of the youngest leaves, and 

 their relation to the apical cell of the stem in Sphagnum, 

 lead to the same results which I had previously arrived at 

 from direct measurement of the sides and angles of the 

 three-sided apical cells of the steins of ferns.* In Sphagnum 

 the object is not fitted for direct measurement ; the steep 

 inclination of the arch of the apical surface renders the 

 accurate determination of the length of its edges impracti- 

 cable. It is worthy of mention, however, that in the apical 

 cells of Sphagnum- stems, with f phyllotaxis, the apical angle 

 of the triangle is visibly much more acute than in stems 

 with | or T 5 3 phyllotaxis. Probably in Sphagnum, as in 

 ferns, the change of form which the terminal cell under- 

 goes between two divisions does not depend upon a capa- 

 city for change of form innate in the cell alone, but is 

 caused by the definite expansion of the cells of the second 

 degree adjoining the apical cell. 



The youngest conditions of lateral shoots which have 

 come under my observation have the form of hemispherical 

 arched cells, which are situated on the outer surface of the 

 terminal bud, at a distance of three or four cells in a 

 straight line from the apical cell, near the left margin of 

 the third or the fourth leaf, and above the middle line, in 

 the first case of the sixth, in the second case of the seventh 

 leaf f (PI. XVIII, figs. 16, 17). When a longitudinal sec- 

 tion of a principal shoot is made through the longitudinal 

 axis of the median shoot, and through that of a young- 

 lateral branch, it is clearly seen that the place of attachment 

 of the young lateral branch, together with the cortical cells 

 which lie between it and the next lower cell, occupies a 

 portion of the outer surface of the stem exactly as large as 

 that occupied by the insertion-cell of a leaf together with 

 the cells of the tissue of the stem which are produced from 

 the same cell of the second degree as the insertion-cell; 

 one of the oblique rows in which the elongated cells of the 

 interior of the stem are arranged reaches up to the place of 

 attachment of the branch (PI. XVII, fig. 1; PI. XVIII, figs. 



* 'Abhandl. Kon. Sachs. Ges. d. Wiss.,' v, 642. I shall return to this subject 

 hereafter in speaking of the development of ferns. 



f Considering the leaf as viewed from the outside and from beneath. 



