THE STRUCTURE OF THE CHARACE#. 7 
smooth, but in some species it is netted or pitted, and in others, 
there is a thick granulated layer of carbonate of lime, contained in 
a soft hyaline membrane. 
The five spiral tubes project beyond the summit of the oospore 
into as many free ends, which, together, constitute what has been 
termed a stigmatic-crown, from the erroneous supposition that it 
was analogous to the stigma of a flowering plant. This crown is 
more pronounced in the Charas than in the Nitellas, and it is per- 
sistent ; in the Nitellas it disappears early. 
These free ends of the spiral tubes also show another distinction 
between the two principal divisions of the family, viz. that the 
teeth of the crown in Charas are unicellular, while in Nitellas 
there is a transverse septum dividing each tooth into a pair of 
cells. Braun was the first to point out this character, and he con- 
siders it the best differential character for separating the two genera. 
In the young state of the investing tubes there is a continuity 
between the prolongation at the free end, and the tube from 
which it originates ; but later on a septum appears and fixes the 
limit between each tooth and the tube of which it is the pro- 
longation. 
As the oospore ripens, the upper ends of the twisted tubes form 
a space or chamber immediately between the base of the crown 
and the summit of the oospore within ; this chamber is closed 
below by a diaphragm in which a narrow opening is said to form 
the communication between the upper chamber and the papilliform 
summit of the oospore. 
The portions of the five tubes which form the walls of this 
chamber then separate from each other, so as to produce narrow 
slits or openings, through which the antherozoids make their way 
to the uppermost of the two cells which compose the inner portion 
of the oospore. 
Good figures, showing the way in which the antherozoids effect 
an entrance through these slits, are given by Pringsheim in the 
plate issued with the Monatsbericht d.k.p. Akademie de Wiss. 2u 
Berlin for May, 1871. So much for the external parts of the oospore. 
Its inner portion consists of an ovoid or globular body contain- 
ing two cells with tolerably thick walls formed of cellulose; the 
longer of these two cells is filled with a colourless fat and with 
grains of starch. The starchy granules were at one time considered 
to be sporules, but erroneously. 
When ripe the oospore drops away from the parent plant and 
falls to the bottom of the pond ready for germination in the autumn, 
or after the winter cold. 
VIII.—GERMINATION OF THE OOSPORE. 
The mature oospore contains two cells, a nodal cell and a basal 
