280 Phillips on a Comparative Study of the 
iodine and sulphuric acid. As it grows older it loses this 
property, apparently from its being changed, or impreg- 
nated by some substance which is negative to all cellulose 
tests. It seems to be allied to fungus-cellulose, though 
Macchiati (50) considered it and the sheath to be the same 
as the cuticle of the higher plants. Correns (18) was able 
to get a cuticular reaction for it with an alcoholic solution of 
chlorophyll. The present investigation gave no reaction 
sufficiently marked to warrant the substance being termed 
cuticle, though the two may have close affinities. 
The walls are laid down in distinct lamelle by the addi- 
tion of microsomata of cellulose upon their inner faces. 
Ambronn (1) found that there was a substance between 
the lamina of cuticular sheaths which disappeared upon boil- 
ing and reappeared when the plant was cooled. He, there- 
fore, concluded that the substance had melted. Hegler (38) 
found that the laminz retained their identity when heated 
in glycerin until the boiling point of the fluid was reached, 
which is much higher than that of water. In such forms as 
Nostoc, Anabaena, etc., all of the lamellz, except the one 
immediately enclosing the protoplast and possibly at times 
a second, swell up and become a thick gelatinous protective 
zone. If a little care be taken in crushing out the colonies 
of Nostoc, this zone can easily be traced to consist of the 
successive generations of lamellz, thus the inner unswollen 
wall which was formed last invests but a single cell. The 
one immediately outside it invests two cells, while the others 
in order will invest respectively four, eight and sixteen cells 
each. When these swollen sheaths are knotted up together 
they make the apparently homogeneous jelly of the Nostoc 
colony. 
In some forms, as Lyngbya, the outer sheaths do not 
gelatinize, but remain tough and thin. If Lyngbya be culti- 
vated in a weak solution of palladious chloride (1 :100,000) 
or in platinum chloride of the same strength, this laminated 
structure is beautifully demonstrated, and the laminz are 
