Fructification forming a large oblong or linear sorus between the base and middle of the frond, of a rich red-brown colour when held between the eye and light, imbedded in the thickened substance of the frond, which decays with it. On a transverse section the soriferous lamina is seen to be hollow in the centre; or rather the sorus is formed of two parallel plates, each covered externally with densely aggregated spores, which occupy what are the uperficial cells of other parts of the frond. Below the superficial series of cells, and especially in fertile specimens beneath the spores, are several, 4-6 or many more, air-cavities, reposing on, and separated from each other by a loose cellular tissue, which is hexagonal, transparent, the cells becoming transversely elongated and finally towards the centre of the frond breaking up into a layer of matted filaments, which surrounds the cavity, a structure resembling very closely that of Fucus confiuens as given by Turner. When thy, the surface of the plant is covered with white efflorescence, similar to that of Laminaria saccharina, it has been analysed by my friend Mr. Stenhouse of Glasgow, who finds it to contain excellent Manna, and who further informs me that this and the other larger Antarctic Alga are peculiarly rich in Iodine.
The Lessonia quercifolia of Bory, is described and figured as having the frond covered with cavities containing spores, whence it woidd appear to belong to Fucoidea, and to be more allied to Z>' Urvillea than to this genus.
Lessonia ciliata of Postel and Rupprecht, is certainly only the young state of Macrocystis pyrifera.
Plate CLXVII. — CLXVIII. — C. transverse section of frond in fructification :— highly magnified.
3. Lessonia ovata, Hook. fil. et Harv. ; stipite brevi vage dichotoine ramoso, ramis brevibus divaricatis, frondis laciniis breviter petiolatis, petiolo in laniiiiani ovatam lineari-ovatamve olivaceo-fuscescentem, submembranaceam dilatato. (Tab. CLXVII.— CLXVIII. B ; et Tab. CLXXI. C.)
Hab. Hermite Island, Cape Horn, and the Falkland Islands; very abundant.
Radix e fibris perplurimis crassis iutricatis massam 1-2 ped. latam efficientibus. Stipites e radice pluriini (ut in Macrocysti) 4-6 unc. longi, torti v. flexuosi, crassitie pollicis humanas, dichotome fissi, demum solitarii, incrassati, subarborescentes. Lamina pedales, colore et substantia L. fuscescentis, juniores basi obscure sinuato-dentatae; adultae integerrima?.
Certainly very near L. fuscescens ; but as far as could be judged on examining the plant, both on the shores it inhabits and in the herbarium, it has good claims to be considered a distinct species, especially in the many short stipites, short branches and broad leaves. Never having seen the fruit, however, it may prove the young of L. fuscescens, for we can well suppose only one out of the many stems of that plant to attain any great dimensions, and the lamina of the young state to be broader than that of the adult.
The ramification of all the species of Lessonia is dichotomous ; each plant in a young state consists of a few rooting and clasping fibres, giving off a single stem (or petiole) and frond. This frond splits at the base, and as the growth proceeds, the fissure extends vertically upwards, till the original frond is bisected ; each of the two parts is now a complete frond, altogether similar to the primary one, and provided with a petiole of its own: these again divide, and the process is repeated. Hence the rapid growth of this genus, and hence the origin of the flattened form of ramidi and elliptic core which is placed in the long axis of these rarnuli and across the axis of the terete stem. It was not observed, whether any relation existed between the number of branches on the whole frond and of concentric rings in the trunk. The latter are probably the indices of the number of times that a subdivision of the laminae has occurred, supposing that all split at about the same epoch, rather than a register of the years the vegetable has existed ; as the following account of the anatomy of this species will show.
A branched portion of the plant, terminated by four laminae, necessarily presents subdivisions of three periods of growth: 1st, the petioles of the four laminae; 2nd, the two rarnuli from which the four are given off; and 3rd, the one branch which gives off the two latter : these were successively examined.
1. The base of the lamina or petiole is exceedingly compressed, and composed of a mass of cellular tissue of
