140 



THALLOPHYTA. 



[CH. 



records how a captain of a brig employed his crew for two 

 bitterly cold days in collecting Lessonia stems which had been 

 washed up on the beach, thinking they were trunks of trees fit 

 for burning. On our own coasts we are familiar with the 

 common Laminaria, the large brown seaweed with long and 

 strap-shaped or digitate fronds which grows on the rocks below 

 low- tide level. The frond passes downwards into a thick and 

 tough stipe firmly attached to the ground by special holdfasts. 

 A transverse section of the stalk of a fairly old plant presents 

 an appearance not unlike that of a section of a woody plant. 

 In the centre there is a well-defined axial region or pith 

 consisting of thick walled, long and narrow tubes pursuing a 

 generally vertical though irregular course, and embedded in a 

 matrix of gelatinous substance derived from the mucilaginous 

 degeneration of the outer portions of the cell-walls. The greater 

 part of such a section consists, however, of regularly disposed 



Fig. 29. A, Transverse section of the stipe of a Laminaria, slightly enlarged. 

 B, A small piece of the tissue between the central 'pith' and 'cortex' 

 showing the radially disposed secondary elements more highly magnified. 



rows of cells which have obviously been formed by the 



