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 Dictyonewron, 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 
Alaria type, to which the 
genera Pterygophora, Eck- 
lonia, Ulopterya, Eisenia, and 
LEgregia conform, also posses- 
ses compound fronds; these, 
‘ however, do not arise by a 
Fic. 15.—Postelsia palmaformis. process of splitting, but by 
outgrowths from the meri- 
stematic cellsat the growing-point. In Alaria 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 
