180 NOTES ON THE HISTOLOGY OF POLYSIPHONIA FASTIGIATA, 
careful examination of fresh fronds Mores a Zeiss te oil immersion) 
shows no continuity whatever. n the “plug” and the 
sree oe on either side fine HFS sts are Siisainiy visible, 
and is are pee into or on to the “ plug,’ as seen on 
side view. If the frond be treated for a few minutes with mineral 
acid, the cells are separated, and the nature of these stris becomes 
re The “ plug” is practically a cork closing the end of the 
c 
« fibrillar thickenings” (as described by inane and Boo 
Spongocladia),* running from the borders of the “plug” up the 
sides of the canal. If the frond, after treatment with a macerating 
reagent, be gently crushed, the ‘‘ plug” separates from one or both 
cells, and the fibrillar thickenings may then be made out as a 
delicate fringe of fine threads arising from the margin of the 
“plug,” and quite independent of the protoplasmic contents of the 
canal sits 304, fig. 11). I have observed this in cells only 10 or 12 
articulations from the apex of the frond. Isolated ‘ plugs” show 
the cover arek ae by Massee (l.c.), while young “ plugs”’ 
show as well one or two distinct hig which are entirely 
absent from the “old er ‘plugs take to be the true 
ean through which continuity of is ~otopiaetirt in young cells is 
ntained ; whilst the granulations of older and completely formed 
rien” are due to unequal or heterogeneous deposition of the 
substance of which the plug is ee ed (fig. ne 
of protoplasm surrounded by a gran dialed ‘* primordial utricle,”’ the 
into granular adaxial plate, and a denser abaxial portion, 
from the ends of which arise the intercellular protoplasmic threads 
CH the eyoung state), or the projections which represent these (in 
( ON: The Bovine of development and escape of the tetraspores.— In 
describing the tetraspores of P. urceolata and P. atrorubescens, 
Wright ( (i, ie) says that their point of origin =e to be always 
central cell and its surrounding cells, a portion 
ie ri ma Bait detached from the ns eal, which ees 
then divides transversely, the lower part f ming a inute 
parallelogram,” and the upper becoming com pletely divided i into 
four tetraspores. The tetrasporangium and the “ parallelocram ” 
have, at least in the young condition, protoplasmic continuity, 
W. ich, ich Ne becomes pte d later on by t plug- 
see (l.c.) an erup Rosenvinge+ describe 
the sea cell firet —— from the central cell as subdividing 
(Massee ibes the process as one of “‘budding”’) into two 
* “On the Structure of Spongocladia Aresch.,” Annals of Botany, vol. ii. 
+ “ Bidrag til Polysiphonias Morphologie,” Bot. Tidssk. 1885, p. 11. 
