CHONDRUS. 439 



the youngest part of the shoot. The youngest or most 

 actively growing* part of a shoot is found at the end 

 furthest away from the basal attachment organ. 



A longitudinal section of a young frond should now be 

 cut at right angles to its surface, and rather near a 

 median longitudinal line. The material should be fresh 

 and the sections should be mounted in sea water. These 

 should be examined first, but others can also be 

 examined after being mounted in glycerine (50 per cent 

 solution in water) or glycerine jelly (fig. 7). 



The Central Conducting Cells will be found to be elongated 

 in a longitudinal direction. They are fairly narrow, and they 

 possess fairly thick walls. The peculiar nature of the 

 walls becomes very apparent when a section is mounted 

 and examined in fresh spring water. In this case, 

 owing to the rapid absorption of water by the cell walls, 

 the sections rapidly curl up. 



This central tissue of much elongated cells resembles 

 more a strand of interwoven filaments than a close paren- 

 chymatous tissue. By this Chondrus crispus may, as 

 already pointed out, be distinguished from the species of 

 several allied genera. But it has this feature in common 

 with Gigartina mamillosa. 



The cells of the conducting tissue are connected with 

 one another at certain points. These points become very 

 evident if the cell walls of a section have been allowed to 

 swell up in water or dilute glycerine. The cell walls 

 encroach on the cell cavity, leaving only a narrow canal 

 of varying length leading apparently from one cell to 

 another. A fine wall, which does not swell up, is stretched 

 across the canal, thus forming a pit, as we find it in the 

 higlier plants. The pit membrane probably allows of the 

 cytoplasm of one cell communicating with that of the 

 other. On each side of this pit is a small cap, consisting 



