310 Sykes. — Anatomy and Histology of Macrocystis pyrifera and 
A transverse section of this plant is seen in Fig. 48, PI. XXI. A zone of 
secondary cortex of considerable size has been added by the meristematic 
division of the outermost cortical layer, and the cells produced by this 
meristem are seen to be arranged in radial rows. In longitudinal section 
the outer cells composing these radial rows are found to be isodiametric, 
while the inner ones are slightly elongated in a longitudinal direction. 
There is thus a gradual transition, in the length of the cells, between the 
secondary and primary cortex, the outer elements of the latter being now 
more elongated than in Stage i, while the innermost cells have by this time 
attained a considerable length. 
In the cross walls of the secondary cortex the pits are arranged in 
a ring and are much deeper, and also sharper in outline, than are the more 
numerous and smaller pits in the primary cortex. The cells of the 
secondary cortex have also many more pits in their longitudinal walls than 
have those of the primary cortex. 
Many interesting changes have occurred in the primary cortex since 
the last stage. The hyphae running into the medulla originate from 
several of the inner layers of the cortex and separate the cells of which 
these layers are composed, causing them in transverse section to appear 
as if arranged in radial rows. The outermost cells of these rows are square- 
ended and somewhat thick-walled, while the innermost cells have much 
more swollen walls and are dilated at the transverse septa. 
The last of these elements pass gradually into the original medulla 
and, becoming very similar in appearance to the primary pith filaments, 
add considerably to its size. The increase in size of the medulla, due to 
the addition of these secondary elements, is readily seen on comparing Figs. 
46 and 48, PL XXI. I propose to term these elements ‘ inner secondary 
sieve-tubes but it must be borne in mind that they are produced by a late 
development from the already formed cells of the primary cortex, as are 
the so-called secondary sieve-tubes in Macrocystis , and in neither of these 
cases are they ‘ secondary ’ in the sense in which the term is used when 
speaking of secondary phloem in Phanerogams, not being formed, like that 
tissue, from the divisions of a secondary meristem. 
The original medulla presents much the same appearance as that 
described in the last stage. 
Stage Hi. Adidt stem. Fig. 49, PI. XXI, represents a cross section of 
the adult stem magnified to the same degree as are Pigs. 46 and 48. 
It will be seen from the photograph that the secondary cortical tissue 
has greatly increased in amount, yet in longitudinal section the same 
gradual transition from periphery to centre is still noticeable. The 
extent of the primary cortex now bears a very small proportion to that 
of the secondary, and the hyphae arise from the outer as well as the inner 
layers, thus apparently increasing the number of elements in each radial 
