102 Oliver . — On the Obliteration of 
above described smaller and often branched trumpet-hyphae 
are met with in fair numbers. One of these is shown in Fig. 6. 
The sieve-plate is on the lateral wall of the hypha, and 
separates the branch from the main hypha. Callus is present 
on both sides of the plate, quite blocking up the lumen of 
the main hypha, and as a glance at the figures will show, 
formed from the wall. 
After several hours’ treatment with clilorzinc-iodine the 
sieve-plates turn blue, the other cell-walls and the callus 
swell up only and do not change colour. 
By cutting longitudinal sections of young stems of 
Nereocystis the trumpet-hyphae may be seen showing early 
stages in the development of callus. Thus Fig. 8 is taken from 
a stem less than 30 cm. long, and shows callus-formation 
before obliteration is accomplished. On the upper side of the 
sieve-plate callus-formation has gone much further than on 
the lower, and the red colouration (due to corallin-soda) 
extends from the middle lamella to the lumen of the hypha. 
On the under side only one layer of the cell- wall is altered, 
and the relation of this change to the perforations can be 
made out. Of three represented which pierce the inner 
non-callous layer only two proceed through the callous 
layer to the unaltered middle-lamella itself. The third 
one is stopped out by the callus, a fate which would soon 
have overtaken the others. On the upper side all the per- 
forations are stopped out. I have been unable to examine 
younger material than this of Nereocystis since, as there is 
but one species in the genus, herbarium-material is scanty, 
and a certain reserve must be exercised in damaging unique 
specimens. 
Regarding the true sieve-tubes themselves, little need be 
said, since they do not essentially differ from those in 
Macrocystis of which I have had a much greater amount of 
material at my disposal. They arise at the periphery of the 
medulla, and are much branched. Fig. 20 gives an idea of 
their structure before the development of the callus. Running 
down the centre of the tube and spreading over the sieve- 
