THE GEELONG NATURALIST. 11 
stand something of the nature and structure of such plants. As 
their name is legion, it will be convenient to pick out one of these 
plants and find out what we can of its life history, structure, mode 
‘of nutrition, &c. Let us take one of the commonest water plants, 
one that can be obtained in any stagnant pool. On the surface of 
such water a kind of green scum may be observed. If some of 
this be lifted up with a piece of stick it will be seen to consist of 
long green very slender hair-like filaments. Out of these we will 
take one species only namely Spirogyra. 
This plant although a good length requires to be placed under 
‚a microscope in order that its structure may be properly observed, 
yet if a very thin section of any soft plant be carefully examined it 
may be seen that it is entirely composed of microscopic structures 
termed cells, each cell is a tiny mass of protaplasm surrounded by 
an elastic tough bag known as the cell wall, and further it has a 
denser mass inside called a nucleus. It must be remembered that 
these cells seldom measure more than 41th of an inch in diameter. 
The protoplasm mentioned is a jelly like substance which is endowed 
with life, and has the power of changing itself into various substances 
such as sugar, starch, &c.; it can also form cell walls or dissolve 
them when the good of the plant requires it. The Spirogyra plant 
is formed of a number of such cells placed in a single row, and as all 
the cells in the plant are exactly the same, we may now examine 
one in detail. In shape the cell is cylindrical, with flat ends, the 
protoplasm lines the wall leaving a large space between it and the 
nucleus, this space is filled with a mixture of water and mineral salts 
termed cellsap. In addition the cell of Spirogyra has a mass of 
protoplasm beautifully tinged with green wound round and round 
just inside the cell wall. 1t exactly resembles a bright green ribbon 
treated in the same manner. Although this plant has neither roots, 
stem, nor leaves, it is able to absorb the fluids and gases it requires 
from the stagnant water in which it exists, and by means of the 
green protoplasm these fluids and gases are formed into proper 
nourishment. Let us now imagine that the water begins to dry up, 
numbers of the cells are destroyed by the fierce rays of the sun. 
Those cells still under water immediately begin to divide thus, the 
the nucleus breaks into two the halves passing to each end of the 
cell, the protoplasm forms a dividing wall, and thus two cells are 
formed from one, and each then grows to its numinal size. Of 
‚course these two cells in like manner may become four, and these 
again eight and so on but always inalinear manner. Thus as long 
Ps there is any water to cover a single cell the plant may revive by 
division. A further defence against the sun is provided by each 
plant being completely enveloped with a jelly-like sheath. But in 
cases of extreme drought a wonderful provision is made by the pro- 
duction of a zygaspore which has the power of withstanding any 
amount of heat and dryness. Let it be supposed that in the immense 
