84 
LAMINARIACEiE Macrocystis. 
iy. 
1. MACROCYSTIS, Ag. 
Root branching extensively. Stem filiform. Leaves simple, formed by the con- 
tinual splitting of a primary terminal leaf ; developed in secund order along the 
lengthening stem, petiolate, having an air-vessel in the petiole. Spores forming 
irregular, superficial, cloudlike patches on small radical leaves, ellipsoidal, with 
hyaline perispore, surrounded by densely packed, inarticulate, clavate paranemata. 
When fully grown the frond in this genus consists of a much branched root, 
from which rise many filiform, simple or branched stems, naked below ; but fur- 
nished above with numerous, unilateral, lanceolate, petiolate leaves, having their 
petioles enlarged into pear-shaped or oblong air-cells. The lateral leaves have 
their edges directed toward the stem and are so far vertically disposed ; and the 
stem itself, when unbroken, always terminates in an oblique leaf, broader than the 
rest, and having one or more slits in its base. This terminal leaf is the growing 
apex, and from the development of the slits in its base new lateral leaves are 
gradually separated. The whole frond, indeed, much divided as it eventually 
becomes, has been developed from the continual splitting of such a leaf. The 
young stem as it first rises from the root bears at its summit a single vertical leaf, 
destitute of vesicle, serrated, except at a short distance above the base, and having 
the apex generally a little hooked in: its outline is therefore somewhat scymetar- 
shaped. In this leaf, commencing within the margin of its lowest edge, are gra- 
dually formed a series of splits, proceeding from the base and extending upwards 
towards the apex. As each split increases in length, it widens by the onward 
growth of the common base ; and air-vessels begin to be formed in the lower and 
slender part of the segments, which are gradually separated. The splitting process 
continues until the split reaches the margin, at which time the air-vessel is com- 
pletely formed, and the margin of the young segment furnished with ciliseform 
teeth ; and its apex being at length free, it becomes a leaf, only differing in size 
from those lower down on the stem, and which have had a similar origin. 
The fructification is found only on root-leaves which never rise to the surface 
and are destitute of air-vessels. It forms cloudy patches, and contains myriads 
of extremely minute spores. 
The student will find an interesting history of this genus, illustrated by an 
excellent figure showing the development of the leaves, in Dr. Hooker’s Flora Ant- 
arctica , vol. 2, p. 461 — 466, tab. 169, 170, 171. 
1. Macrocystis pyrifera ; Ag. IT o ole. and Harv. in Hook. FI. Antarct. vol. 2, 
p. 461. Macrocystis Humbolcltii , planicaulis , angustifolia , tenuifolia, pyrifera , pela- 
g'tca , luxurians , latifolia , Orbigniana , Auct. — J. Ag. Sp. Alg. p. 155 — 158. Kiitz. Sp. 
Alg.p. 582 — 583 (also M. Dubenii, Aresch., latifrons , Bory, dfc.). Lessonia ciliata , 
Post, and Rupr. Illust. p. 9, t. 38, /. 9- 
