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 w r alls 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. 



Tn 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 its shape, and conse- 

 quently the form of the cavity containing it, 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 continually proceeds so long as life lasts. Every 

 year new branches or twigs with their associated leaves 

 are constantly produced. With such continuous increase 



