deprived of its woody tissue, for it is a stem composed of layer upon layer of cellular tissue, deposited round an axis, which, like the pith, when once formed, is afterwards but slightly modified.
Tlate CLXVII. — CLXVIII. B. apex of branch and frond of the natural size ; B 1, transverse section of young stem : — magnified.
4. MACEOCTSTIS, Ag.
1. Microcystis pyrifera, Agardh, 6);. Alg. vol. i. p. 47. Nov. Act. Nat. Cur. vol. xix. p. 297. t. 26 f. 2. Post, et Ruppr. Iltust. Alg. p. 9. t. 6 ; et p. 4. t. 39. f. 22, 23. Ft. Antarct. Pt. 1. p. 178. M. communis, Bory, in Diet. Class, v. x. p. 8. M. planicaulis, Agardh in Nov. Act. Nat. Cur. I. c. Lessonia ciliata. Post, et Ruppr. I. c. (young state).
Var. /3. integrifrons ; foliis fere integerrimis planis rugoso-plicatisve. M. integril'rons, Bory, I. c. t. 6.
Var. y. angustifrons; vesiculorum parietibus tenuibus, foliis ut in 31. pyrifera. M. angustifrons, Bory, I. c. t. 8. Agardh, I. c. t. 26. f. 4 and 5. Post, et Ruppr. t. 5.
Var. 8. zostercefolia ; foliis anguste lineari-elongatis planis. M. zosterrefolia, Bory, fyc.
Var. f. luxurians ; foliis 3-8-pedalibus S unc. latis basi cordatis membrauaceis plicatis margine longe ciliato-dentatis, vesiculis late obovatis parietibus tenuibus, caule gracili. (Tab. CLXIX. — CLXX.)
Var. £ . membranacea ; foliis ut in M. pyrifera sed tenuissime membrauaceis planis, vesiculis parvis elliptico-ovatis utrinque subacutis.
Var. 77. Humboldtii ; foliis lineari-elongatis planiusculis, vesiculis globosis tenuibus. M. Humboldtii, auct. M. pomifera, Bory.
Hab. Throughout the Antarctic seas, between the parallels of 40° and 64°, both attached, and floating over the whole ocean.
After a very attentive examination of many hundreds of specimens, we have arrived at the conclusion that all the described species of this genus which have come under our notice may safely be referred to Macrocystis pyrifera. Nor can these variations excite surprize, when it is considered that this gigantic weed is subject to every vicissitude of climate, of temperature, and exposure; that it literally ranges from the Antarctic to the Arctic circle, through 120 degrees of latitude; that it lives and flourishes, whether floating or attached, growing in bays, harbours, or the open sea when most distant from land; and, lastly, that it equally adapts itself to the calmest or most tempestuous situations, to waters of uniform depths or those which rise and sink with the tide, to dead water or to strong currents. One thing alone it requires, and that is, a mean depth of six or more fathoms; for, like the Laminarim of our own shores, it, and others of the same tribe in the south, invariably form the outer belt of marine vegetation.
A few remarks upon the above varieties may be interesting ; showing how much their characters depend upon natural causes, and how much more upon mutilations of the specimens, or changes during the operation of drying.
Variety (3. integrifrons. This' we have received from various parts of the west coast of South America ; its characters rest almost entirely on the want of ciliation at the margin of the frond, which is much dependent upon the portion of the plant from which the specimen is taken, the lower leaves being always nearly entire ; also on the state of the waters, those plants which grow in quiet bays having very much developed cilia?, whilst those from the main ocean or stormy coasts are generally more entire.
Variety S. zosterafolia, is a plane and narrow-leaved state of M. pyrifera ; we have traced all the changes in one specimen of M.pyrifera, from very rugose to perfectly plane. Young specimens and terminal leaves are generally
