262 Mr. G. H. K. Thwaites on Tetraspores in Algae. 
the utricular cells of the spore-sac. The primordial utricle is 
however completely isolated in the lower cell, 2. e. the immediate 
elongation of the nucleary membrane itself, the contents of which 
do not consist as before of chlorophylle, but of cytoblastema. 
When acted upon by nitric acid, it frequently contracts so much, 
as to appear torn into large band-lke fragments, which become 
somewhat spirally twisted (fig. 25). Its membrane is not per- 
fectly smooth but finely granular. This does not occur so much 
in the lowest segments of the stem. It is remarkable, that when 
treated with nitric acid, which contracts it considerably, it ex- 
hibits various-sized conical prominences. Hence it appears some- 
what angular or wavy. The small projections appear generally 
to pass into minute depressions on the axial membrane. Ata 
subsequent period a secondary membrane is formed between it 
and the axis. 
From what has been stated, it appears that the stem consists of 
an epidermoidal membrane, subsequently also of a secondary one, 
the primordial utricle and the cell-contents. The above epider- 
moidal membrane, which is the direct elongation of the nucleary 
membrane, continues to grow with the plant, and in such a manner 
that the plant remains init as in abag. Kiitzing calls this mem- 
brane the peridermis, and considers it as identical with.the cuticle 
of Brongniart, which covers the true epidermis of more highly 
organized plants *. There can ‘however be no question here of 
a true epidermis, nor indeed in any of the Alge. 
[To be continued. ] 
XXXV.—On the Occurrence of Tetraspores in Alge. 
By G. H. K. Tawarres, Esq. 
To the Editors of the Annals of Natural History. 
GENTLEMEN, 2 Kingsdown Parade, Bristol, March 19, 1846. 
In the last December Number of your valuable Journal is an 
extract from a letter presented by M. Montagne to the French 
Academy on the subject of an interesting Alga belonging to the 
Zygnemata, and discovered by M. Durieu in Algiers, in which 
the fruit consists of four distinct spores in each sporangium. 
The Rev. M. J. Berkeley obligingly favoured me with a sight 
of an authentic specimen of this species, in which the character 
was very obvious. ) 
On examining, a few days ago, some spores of Mesocarpus sca- 
laris, Hassall, I thought I could detect in them indications of a 
quaternary division, and I sent specimens to Mr. Berkeley for 
* Kiitzing, J. c. p. 86. 
