CHARACE.E. 



281 



of the stem, but is wanting in Nitella. From the basal nodes of each leaf one 

 cortical lobe which is morphologically individuaHsed runs downwards, and one 

 upwards^ (Fig. igg, B,r, r\ /' and Fig. 201). In the middle of each internode there 

 fore as many ascending cortical lobes as there are leaves in the whorl meet with 

 the cortical lobes that ascend from the next 'whorl below. The number of the 

 latter is, however, smaller, ^because the leaf in the axil of which the lateral shoot 

 arises does not form an ascending lobe. The cortical lobes are in close con- 

 tact laterally, and form a closed envelope round the internode, the ascending 

 and descending lobes dove-tailing in a prosenchymatous manner. The forma- 

 tion of the cortex takes place so early that the elongating internode is covered 



Fig. eot.— Development of the cortex of the stem of Chara fragilis ; A a very young internode of the stem with the 

 cortical lobe r still consisting of one cell ; B—D its further development ; r r signifies in all the figures the cortical lobes that 

 ascend from the lower, r' r' those that descend from the upper leaves ; i>v the apical cell of each cortical lobe ; ^^ its inter- 

 nodal cells, n m n the commencement of the formation of the node ; Dc the central cell of a cortic2iI node ; .S signifies in all 

 the figures the unicellular 'stipules' which spring in pairs from the base of the leaves. 



by it from the first, the lobes keeping pace with its extension in length and 

 thickness. Each lobe continues to grow, like the stem, by means of an 

 apical cell, which becomes segmented by horizontal septa ; out of each of the 

 segments cortical internodal and nodal cells are formed by repeated divisions. 

 The latter divide, by successive septa, into an inner cell, in contact with the 

 internode of the stem, and three outer cells, the middle one of which commonly 

 grows into the form of a spine or knob, resembling a leaf. The outer lateral cells 

 of the cortical node, on the other hand, foll'owing the elongation of the internode 

 itself, grow into longer tubes, so that each cortical lobe consists of three parallel 

 rows of cells, the middle row however containing alternately short and long (inter- 

 nodal and nodal) cells. The cortex of the leaves is derived from the leaflets, 

 and its formation is much simpler (Fig. 200, C-E, br). From the basal nodes of 

 Chara other foliar structures also arise, both on the inner and outer side of the 

 base of the leaf (Fig. 199,6'), which Braun calls Stipules ; they are always unicel- 

 lular, and are sometimes very short, somethnes elongated. 



* The first internode of every branch and leaf becomes covered with a cortex derived only 

 front! the descending cortical lobes of the next node above. 



