the Sieve- tubes in Laminarieae . 103 
plates is the contracted protoplasmic content of the tube. 
Gradually as they get older callus is formed, and the pores 
obliterated. My description of the same structures in 
Macrocystis must however suffice. 
Macrocystis pyrifera , A g. — The best general account of 
this plant is given by Hooker and Harvey 1 . According to 
these authors all the different species are in reality varieties 
only of M. pyrifera. Many so-called species may be found 
growing on the same plant. It is an inhabitant of antarctic 
seas between lats. 40° and 64° S. It is found extending along 
the Pacific coast of America as far north as California and the 
Aleutian Islands ; on the Atlantic side, not beyond the Plate 
River, lat. 35 0 S. Its immensely long stems, reaching to 300 
metres, and leaves with bladders, are too well known to require 
further description here. Regarding its fructification, all that 
is known is that within a few centimetres of the root, sub- 
merged leaves 2 , destitute of floats, are formed with sori, 
consisting of patches of ‘ spores.’ 
Anatomy of Stem. — In the general anatomy there is no 
essential point in which it differs from Nereocystis. The 
outline of the central medulla is usually oval rather than 
round. In almost all cases the zone of true sieve-tubes com- 
pletely encloses the axile hyphal strand ; this I found a 
constant character in 26 out of 28 specimens examined. The 
only exceptions were Macrocystis planicaulis , in which at one 
side of the medulla the hyphal tissue ran into the cortex, the 
zone of sieve-tubes being discontinuous at this spot ; and in 
a specimen of Macrocystis angustifolia , in which a most in- 
teresting arrangement was met with. The transverse section 
was crescentic, the dorsal side concave, the ventral convex. 
The medulla, oval in outline, was situated so that its longest 
axis coincided with the plane of symmetry (median plane). 
On all sides except the uppermost it was enclosed in a zone 
of sieve-tubes, but at this point the inner hyphae came into 
1 Hooker’s Flora Antarctica, vol. ii. p. 461. 
2 Cf. Gardiner, On the occurrence of reproductive organs on the .root of 
Laminaria bulbosa , in Proc. Camb. Phil. Soc. vol. v (1885), P* 22 4 - 
