Laminaria sac char ina. 
303 
there can be little doubt that Setchell 1 is referring to elements of this 
nature when he describes the transformation of some of the anastomosing 
hyphae of Sacchoriza into conducting-tubes. 
B. Histology. 
i. Nature of cell-walls. 
The mucilaginous nature of the cell-walls of both cortex and 
medulla in Macrocystis is well shown by their great affinity for Methy- 
lene blue. In this and other respects, however, both the pit-closing 
membranes of the cortical pits, and the sieve-plates, show a marked 
difference in reaction from the rest of the walls. The pit-closing mem- 
branes do not stain at all with Methylene blue, but the sieve-plates, 
with the exception of the small areas actually traversed by threads and 
slime-strings, take up the stain after remaining in it some hours ; cf. Fig. i, 
PL XIX. " 
With Congo red the outer layers of the cell-wall stain pink, but the 
middle lamella, pit-closing membranes, and sieve-plates remain unstained. 
The cell-walls of both cortex and medulla give the ordinary cellulose 
reaction with Iodine and Sulphuric acid, but the middle lamella is very 
resistant, and remains yellow for a long time before it turns blue, whilst the 
actual membranes of the pits and the sieve-plates remain permanently 
yellow. 
In their response to swelling agents, it is found that the pit-closing 
membranes and sieve-plates differ from the cell-wall. Picro-sulphuric and 
other acids cause the latter to swell considerably, but produce little or no 
result on either of the former. A solution of Iodine in Potassium Iodide, on 
the other hand, has not so marked an effect on the cell-wall, while pro- 
longed treatment with this reagent finally causes the pit-closing membranes 
and sieve-plates to swell slightly. No swelling agent yet used has been 
able to overcome their powers of resistance to any great extent. 
From the above it would appear that the chemical nature of the 
cell-wall is of the following constitution. The middle lamella is chiefly 
composed of pectic compounds with some cellulose, but in the outer 
layers of the wall the proportion of cellulose to pectose is increased. The 
pit-closing membranes and sieve-plates are evidently composed of some 
substance still more resistant than pectose. 
ii. Protoplasmic continuity in cortex and hyphae. 
a. Cortex. The demonstration of protoplasmic connecting-threads in 
the cortical cells of Macrocystis is, owing to the resistant nature of the pit- 
closing membrane, a matter of some difficulty, but satisfactory results were 
obtained by means of an adaptation of the Safranin method. 
* Setchell, 1. c., 1891. 
