THE HIGHER CRYPTOGAMIA. 91 



rules ; each shoot originates from the blending together of 

 three sub-shoots, and has only a limited growth. New 

 shoots are only formed in the two incisions which the fore 

 edge of each fully developed wedge-shaped shoot exhibits. 

 All shoots, with the exception of the first, which proceeds 

 directly from the spore, undergo complete distortion, caused 

 by the peculiar growth of their median portion and by the 

 expansion of the next younger shoots of a new order, 

 which originate in the incisions of the fore edge of each, 

 and which amalgamate with the median portion ; their 

 form passes from a pointed semi-oval, through that of a 

 wedge, to a furcate shape. The repeated furcate ramifi- 

 cation of young plants soon renders their entire outline 

 circular. 



The multiplication in a longitudinal direction of the 

 cells of each of the three parts of which a shoot is com- 

 posed takes place through the division of the cells of the 

 fore edge by means of transverse septa inclined to the 

 horizon (PI. XIII, figs. 7\ 14). The multiplication is much 

 more active in the median line of the young shoot than at 

 its sides. The cells of the second degree divide by septa 

 almost parallel to the upper and under surface of the shoot, 

 and this division is repeated in the outer of the newly 

 formed cells, by which means the shoot increases in thick- 

 ness. Immediately after the appearance of the first of the 

 above septa each of the two cells which have originated 

 from the division of each upper cell of the second degree 

 is usually divided into two by the formation of a transverse 

 septum, perpendicular to the outer surface, and cutting the 

 longitudinal axis of the shoot at an angle of 90° (PI. XIII, 

 fig. V). The cells of the upper half of the flat stem are 

 consequently, even in their earliest stage, usually one half 

 shorter than those of the under half. It is only in those 

 shoots in which the longitudinal growth is especially active 

 that the transverse division of the cells of the under half of 

 the stem lags behind that of those cells of the upper 

 surface which are situated further back from the fore edge 

 (PI. XIII, figs. 11, 14). Such shoots are usually those 

 which bear the archegonia. The growth in thickness, the 

 division by septa parallel to the surfaces of the shoot, is far 

 more active in those cells which are produced by the 



