IN VEGETABLE BIOLOGY. 609 



ing axial cell, communication is ensured by the agency of a fila- 

 ment, slender at first, but rapidly increasing in calibre. In 

 the earliest condition observed by me a bright point of plasma 

 has made its appearance at the top of the protoplasm upon the 

 contiguous faces of the ultimate and penultimate cell; these 

 points rapidly grow, and soon form a small ring through which 

 the connecting filament passes. After the formation of several 

 axial cells the branch becomes corticated : the first step in this is 

 the shutting-off, except for a fine filament, of a small cell from 

 both the upper and under face of the axial cell at its distal end. 

 A couple of small wing-like cells then make their appearance, 

 one on each side of the proximal wall of the new cell, with which 

 latter they remain in filamentary connection. Meanwhile the 

 basal cell of the branchlet on each side has lengthened down- 

 wards, and, dividing transversely, it occludes from the external 

 world the side of the axial cell. At the proximal end of the* 

 latter small cells are now budded off, the whole of the cells thus 

 formed repeatedly dividing and growing into a firm cortex round 

 the axial cell. Since every cell remains in permanent filamentary 

 connection with its parent, it follows that there is continuity in 

 one way or another throughout the thallus. 



Before cortication has advanced to such a stage as to shut out 

 the axial cell from sight, the continuity of the axial cells has 

 plainly become indirect. Fig. 33 shows a surface view of a ring 

 in this condition, its membrane having a couple of pores. Further 

 down the evidence of indirectness is much clearer. Fig. 34 a is 

 a view in longitudinal, and fig. 34 b one in transverse section, of a 

 well-grown axial cell. In consequence of the tenacity of the 

 protoplasm (a fact of such constant occurrence in the Florideae) 

 demonstration of continuity is very difficult. The longitudinal 

 section shows a broad ring, from either side of whose circumfer- 

 ence stretch threads and films of protoplasm to join the proto- 

 plasm of the cell. In the transverse section a number of threads 

 are seen passing into fine pores upon the circumference and just 

 within the contour of the ring. The ring is stopped with mem- 

 brane upon which filmy cell-protoplasm can in some parts be 

 seen ; it is probably this which prevents a sight of the pores all 

 round the ring, for the pores can be traced with tolerable ease 

 where there is no overlying protoplasm. Near the centre is a 

 bright point which may also mark the position of a pore. The 

 axial cells communicate with their daughter cortical cells by means 



