212 CURREY, ON FRESH-WATER ALGH. 
3. The next plant which I have to mention, is one which 
has not hitherto been observed in this country.* I have only 
found a single specimen, and that in a young state, but 
there is no difficulty in identifying it with the species de- 
scribed by Dr. Braun, in his ‘ Algz unicellulares,’ under the 
name of Sciadium arbuscula. 'This Sciadium arbuscula is an 
Alga of very singular growth. It consists, in its first stage, 
of an erect cylindrical elongated cell, furnished with a very 
short narrow stem at the base. ‘The endochrome of this cell 
breaks up into separate portions and forms, from five to ten, 
usually eight, gonidia, arranged at first in a single row. 
Afterwards the apex of the cell opens by a circumscissile fissure, 
and the gonidia protrude through the orifice and form an umbel 
of cells. The cells forming this umbel grow into elongated 
cylindrical cells, precisely similar to the parent-cell. Their 
stems are united into a fascicle just mside the mouth of the 
tube of the mother-cell, but are not long visible, owing to a 
dark-coloured secretion, which forms round the bases of the 
cells at an early period of their growth and completely ob- 
scures the stems. The branches of the primary umbel pro- 
duce gonidia, which go through the same process, and thus 
secondary umbels are formed, from which, in process of 
time, tertiary umbels are produced. ‘The gonidia which are 
formed in the branches of the tertiary umbels, instead of 
remaining united at the apices of the branches, escape from 
their mother-cells, but it is not certain whether they emerge 
in the form of zoospores, or as motionless cells. Dr. Braun 
has not observed their actual escape, but has seen zoospores 
agreeing in size and form with the gonidia of Sciadium 
moving about, amongst the specimens of that plant, and 
which, in his opinion, had their origin im the cylindrical 
cells. 
Fig. 10 represents the British specimen which occurred in 
a pool on Paul’s Cray Common, in Kent, in the spring of 
1856. The cylindrical cell was colourless for the greater 
part of its length, but the tip was almost black, having, how- 
ever, a reddish tinge, the colour being so dark as quite to 
obscure the stems of the transparent green gonidia, which 
protruded, eight in number, from the apex of the mother- 
cell. I did not see the short filiform stem noticed by Dr. 
Braun ;+ but, on referring to his figures, it will be seen that 
* I have this spring observed two more specimens in water from the 
same locality, both in the same stage of growth as the one described in the 
text. 
t This stem was plainly visible in the specimens which occurred this year. 
