HOW PLANTS LIVE AND GROW 29 
This is a rough outline of the way in which a plant 
keeps itself alive. Some water-plants do without roots, 
and find all they want dissolved in the water in which 
they live.. Seaweeds, for instance, even take their car- 
bonie acid gas from the water, for there is a little 
dissolved in sea- water, and some flowering plants are 
content with only leaves and stalks. 
Plants grow in two ways; either the cells expand or 
they go on dividing. We have seen how the walls are 
increased by the building protoplasm, but this process 
has its limits, and the chief method is for the cells, like 
those of the cambium ring, to divide themselves into two 
or more. The topmost point of a stem, for instance, 
builds itself higher by this constant splitting, and so 
does the lowest part but one of the root. The very 
end of the root is a mass of hardened cells, which do 
not continue to grow but act as a borer, and also as a 
protection for the tender growing part behind them. 
When a cell is about to divide, the first noticeable 
feature is that the “nucleus,” or thicker portion of the 
protoplasm, splits into two, or, if four new cells are to 
be formed, into four sections. Then a new cell-wall, 
or new cell-walls, will be rapidly built, and each cell 
may start dividing again (see illustration on p. 11). 
In some of the lower plants the nucleus may divide 
into an indefinite number of nuclei, and, each with its 
surrounding little globule of protoplasm, all may be 
driven out into the surrounding air or water to build 
fresh walls around themselves, and to start as new 
individual plants. 
It would seem, perhaps, that the power exerted by a 
mere jelly could not be very great, but the number of 
cells is so large that, when they work together, hardly 
