78 SEAWEEDS 



in length, until at last there are two blades, each 

 with its own short branch and its own growing- 

 point. The primary blade thus has its place taken 

 by those split off from it, and these again and again 

 by others. In Dictyoneuron, which is unbranched, 

 the long narrow, veined fronds become divided into 

 two by the splitting at the 

 growing-point, and the fis- 

 sure extends almost to the 

 base of the stalk, so that 

 little of a common stalk is 

 left. This portion frequently 

 becomes covered with root- 

 lets, so that the ultimate 

 appearance is that of a group 

 of separate plants. The 

 Alar ia type, to which the 

 genera Ptcrygophora, Eck- 

 lonia, Ulopteryx, Eisenia, and 

 Egregia conform, also posses- 

 ses compound fronds ; these, 

 however, do not arise by a 



PIG, Yo.-Po^Msiajpalmcpformis. process of Splitting, but by 



outgrowths from the meri- 



stematic cells at the growing-point. InAlaria there 

 is a large terminal blade and a simple short stalk 

 with a growing-point in the usual place, but on the 

 upper portion of the stalk there are two rows of 

 leaflets or sporophylls, on which alone the sori of 

 sporangia are borne. These sporophylls arise as 

 outgrowths from the lower region of the meriste- 

 matic cells constituting the growing-point, and as 



