16 



the curve of tlie assiniilatino- filaments of tlie shoot. Tlieu 

 again, near the periphery of the whole attachment organ, 

 where the latter is still very thin, the curved rows of cells 

 have their convex sides turned towards the margin. Seen 

 in surface view the cell rows are observed to o-row out in 

 a fan-shaped fashion towards the margin. 



The growth of the rows of cells is here mainly, if not 

 exclusively, apical. Transverse divisions in the apical 

 cells are common, longitudinal at the most extremelv rare. 

 The upright rows of cells will be seen to be completely 

 undivided (fig. 10). 



The whole attachment disc grows in circumference by 

 the formation of new rows near the margin. But it grows 

 in thickness by the elongation through apical cell forma- 

 tion of the old cell rows. The cells once formed do not 

 change their form and size to any great extent, as soon 

 as they have attained their full size, about o to 4 cells 

 behind the tips of the filaments. 



The whole plant is covered b}' a protective membrane, 

 which is not very thick in older shoots, but is very 

 distinct near the apex of a shoot. It becomes a very deep 

 layer in certain parts of the basal attachment organ. On 

 either side of the insertion point of an upright shoot, it is 

 usually very well developed. It is here produced by 

 successive layers of wall substance being separated off 

 from the apical cell of each filament (Pi. III., fig. 10). 



The cells of the attachment organ are usually full of 

 starch. They are reddish in colour, but the latter is not 

 as dark as in the assimilating cells of the upright shoot. 



3. — Histology of the Shoot. 

 The cell walls of the central cells are not very thick 

 when examined fresh and in sea water (PI. II., fig. 8). 

 They do, however, swell up very much in spring water 



