52 TYPES OF BRITISH PLANTS 
when a family is required, a transverse wall is run up 
across one end of the tube, making a nursery, so to speak. 
On the outside of the tube are developed two separate 
organs, one thin and curved like a horn, and the other 
round. In the latter masses of protoplasm are separated 
off, but they do not leave the mother-cell until other 
pieces have been expelled from the horn, which descend 
upon them and give them the desired ability to construct 
a cell-wall for themselves. 
As a last example we may take almost the highest 
of the alge, the Stoneworts. These appear to have ad- 
vanced so far as to have leaves, for they have whorls 
of leaf-lke appendages at the joints of the stem, but 
these are not sufficiently different in structure to count 
as true leaves, though we are approaching very near. 
The Stoneworts may be found in almost any gently-— 
moving water, and especially on the Norfolk Broads, 
where they form a dense carpet upon the muddy bottom. 
So numerous are they that as they rot they steadily 
make the water shallower and shallower, for their 
decaying plants contain a great deal of lime which 
they have drawn from the water, and it all tends to 
silt up the channel. This process can be seen at work 
rapidly on such broads as Hickling and Ranworth. 
Besides their claims to respect by reason of their 
attempt at leaves, the Stoneworts are distinctly high- 
class in their fructification. On the leaf-lke appendages 
are formed two kinds of organs, corresponding to those 
of Vaucheria and the Bladder-wrack. The father in 
this case is a spherical orange body, contained by eight 
plates which lock into one another and enclose, springing 
from their inner side, long hairs. These hairs consist of 
strings of cells, in each of which is a small piece of 
f at 
