84 LAMINARIACE^.— Macrocystis. 



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 

 ]3etioles 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 cilia3form 

 teeth ; and its apex being at length free, it becomes a leaf, only dififering 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, l7l. 



1. Maceocystis pyrifera ; Ag. Hooh. and Harv. in Hook. Fl. Aiitarct. vol. 2, 

 p. 461. Macrocystis Humholdtii, planicaidis, angustifolia, tenui/oUa, pyrifera, pela- 

 gica, luxurians, latifolia, Orhigniana, Auct. — J. Ag. Sp. Alg. p. 155 — 158. Kiitz. Sp. 

 Alg. p. 582 — 583 (also M. Dubenii, Aresch., Iatifr07is, Bory, ^-c). Lessonia ciliaia. 

 Post, and Rupr. Illiist. p. 9, t. 38, /. 9- 



