p o s t e i s i a 207 



ture, the Egregia plant in which the 

 process of longitudinal splitting has 

 also gone on looks like a tuft of fringed 

 straps, thirty or more arising from a 

 single holdfast and prolonged twelve 

 or fifteen feet into the water. 



Another modification of the primi- 

 tive leaf which should be mentioned is 

 the perforation which takes place in 

 laminae of Agarum and Thalas stop hy Hum, 

 so that the mature frond has the appear- 

 ance of a porous plaster. Agarum, in- 

 deed, is known as the "sea colander" 

 on account of this peculiarity. In Cos- 

 tarica and Dictyoneuron the lamina be- 

 comes strongly ribbed or reticulated, 

 while in many of the genera the lamina, 

 at first thin and homogeneous, becomes 

 at an earlier or later age provided 

 with a midrib. In some of the species 

 the general surface of the lamina 

 remains smooth, as in all the young 



