312 Sykes . — Anatomy and Histology of Macrocystis pyrifera and 
(b) Histology. 
i. Nature of cell-walls. 
The cell-walls in Laminaria saccharma are of an even more muci- 
laginous character than those of Macrocystis , and hence they stain very 
strongly with such reagents as Methylene blue, but more faintly with 
Congo red ; with Iodine and Sulphuric acid the outer layers of the cell- 
wall rapidly turn blue, but the middle lamella first takes a yellow tinge, 
and afterwards turns blue like the rest of the wall. 
The pit-closing membranes, as in Macrocystis , differ in their reactions 
from the general cell-wall. They become yellow when treated with Iodine 
and Sulphuric acid, and do not stain at all with Methylene blue or Congo 
red. The distribution of the pits in the cortex has been described above, 
but a more minute investigation of their nature shows that each primary 
pit is made up of a number of secondary pits ; Figs, i and 2, PI. XX, represent 
transverse walls of cells of the secondary cortex, and are drawn from prepa- 
rations stained with Methylene blue. The general wall is deeply stained, 
but the pits appear as rounded areas in which are blue lines on an un- 
stained ground. The blue lines separate the secondary pits from one another, 
while the spaces between them, which are left unstained, represent the pit- 
closing membranes of the secondary pits. The distribution of the connect- 
ing-threads is found to be practically confined to these unstained areas. 
The sieve-plates, like the pit-closing membranes of the cortical cells, 
are of a more resistant nature than the general cell-walls. They turn 
yellow when treated with Iodine and Sulphuric acid, and do not stain with 
Congo red. After remaining for a short time in a solution of Methylene 
blue they present the appearance of a delicate reticulum, the meshes of which 
are blue, while the spaces between, which correspond to the areas traversed 
by the threads, remain unstained. The transverse walls of the young 
primary cortex, from which some of the sieve-plates are derived, give a 
similar reaction. 
ii. Protoplasmic continuity in cortical cells and hyphae. 
a. Cortex. In the outer secondary cortex the connecting-threads are 
always arranged in definite groups, almost, if not entirely, confined to the 
pits. A surface view of the cross wall of a cortical cell shows five to eight 
of these groups arranged in the form of a ring near the periphery of the 
wall, as seen in Fig. 3, PI. XX. Each pit in the longitudinal wall is traversed 
by threads which here also are arranged in clusters (Figs. 6 and 7, PI. XX). 
In the inner secondary cortex the pits often extend much further 
towards the centre of the cross wall, and, when such cases are examined for 
threads, it is seen that, while groups of threads are present corresponding to 
the pits, a few isolated threads are also found in the other parts of the wall 
