THE SKELETON OF THE PLANT 37 
tion of every new cell being completed at once by the 
membrane which is formed as soon as the protoplast has 
divided into two. This is particularly noticeable in cases 
where a cell-complex or community forms the plant-body. 
Each protoplast thus continually forms for itself a chamber 
to dwell in, the walls of which at first, at any rate, are 
probably all alike. We may thus recognise in the cell-wall 
an exoskeleton for the individual protoplast, which may or 
may not undergo subsequent modification. 
In the case of a large plant consisting of innumerable 
protoplasts, the cell-walls of the separate units are found 
united together in different ways, and to a different extent 
in different individuals. The resulting network constitutes 
at first the skeleton ‘of the whole plant. The modification 
of the cell-wall which was unnecessary so long as the 
protoplast was solitary, becomes imperative as soon as the 
needs of a large community are established, and secondary 
differentiations of such cell-walls result, the alterations 
being due, like the original formation, to the activity of 
the protoplasts. Not only are the walls changed in 
substance and in thickness after they are formed, but the 
protoplast itself frequently alters the form of the cavity 
containing it, and consequently its own shape, by irregulari- 
ties of subsequent growth. The skeleton of the plant is 
not therefore merely the hard tissues which will survive 
maceration and desiccation, not merely those coarser 
structures evidently set apart for protection and support, 
but it includes all the delicate cell-walls which form the 
cavities in which the protoplasts are living. We may 
indeed discriminate between the skeleton of the individual 
protoplast and that of the large community of which it 
forms a part. 
The skeleton of a large plant such as a tree increases 
in complexity as its life continues. In such a plant 
growth proceeds continuously so long as life lasts. Every 
year new branches or twigs with their associated leaves 
are constantly produced. With such continuous increase 
