CHARACE^E 175 



whorl, which subtend the branches, are arranged in a spiral line running 

 round the stem ; but this is not the case with the branches or secondary 

 axes, where the members of contiguous whorls are superposed. 



The Characeas exhibit in an especially clear and beautiful manner 

 the phenomenon of cydosis, or rotation of the protoplasm (see fig. 163). 

 The best objects for observation are the large internodal cells of Nitella 

 (Ag.), the apical cells in the leaves of Chara, or some of those belonging 

 to the reproductive organs, especially to the ' manubria.' The cell first of 

 all develops vacuoles in its protoplasm, which coalesce into a single 



A 



FIG. 162. Longitudinal section through bud of C.fragilis, showing apical cell, /, and segments, g, b. 

 A , cells empty. B, with cell-contents, granular protoplasm, chlorophyll-grains, and vacuoles. C, 

 with cell-contents contracted by iodine ( x 500). (After Sachs.) 



large sap-cavity. The outermost thin parietal layer of protoplasm, in 

 which are imbedded most of the grains of chlorophyll, remains motion- 

 less; within this motionless lining is a thick layer of protoplasm, in which a 

 regular current gradually sets up, up one side of the cell and down the other; 

 the boundary between the two currents being marked by hyaline bands 

 entirely destitute of chlorophyll, the neutral zones, in which no movement 

 is visible. The direction of the rotating movement in each cell stands 

 in a definite relation to that of all the other cells of the plant. From 

 time to time the movement ceases, and then begins again in the oppo- 

 site direction. Before the rotation commences the cell-nucleus has 



