CODIUM. 300 
grown plant average from } to 2 of an inch in diameter, 
narrower at the base and swelling out somewhat at the 
apex. The apices of the branches are obtuse and much 
darker in colour than the rest of the plant. Occasionally 
the fronds are somewhat compressed. In length they 
vary greatly. We have found, after examination of a large 
number, that a well grown plant (in this district) 1s on an 
average from 8 to 10 inches long, but Harvey speaks of 
them as sometimes reaching a length of 2 feet. The plant 
he figures, however (Phyc. Brit., Pl. XCIII.), 1s under 
8 inches in length, so that our plants may be taken as of 
normal size for the British Islands. 
In colour Codiwm tomentosum is a rich dark green, 
intensely so near the apices of the branches—so dark, 
indeed, as to appear almost black. This will be found to 
be due to, first, the closer packing of the superficial palisade 
“cells” in these localities, and secondly, to the aggrega- 
tion of the chioroplastids in the apices of the palisade 
“cells”’ themselves. The green is not so intense nearer 
the base. In substance the plant, when fresh, is fairly 
firm and rigid, and, externally, soft and slippery to the 
touch; but after preservation in alcohol it becomes soit 
and flaccid. 
ANATOMY. 
A. VEGETATIVE ORGANS. 
The thallus consists essentially of densely woven 
branched hyphe, forming a central core or medulla, from 
which arise very numerous short and thick branches, 
standing at right angles to the long axis of the branch and 
closely packed so as to form a velvety pile covering the 
entire surface. 
The plant is attached to the substratum, as already 
stated, by numerous rhizoids. The rhizoids are branched 
