The requirements of the several protoplasts must be met by supplies from without, and, as many of them are deep seated, varieties of need arise, so that various members of the colony are set apart for special duties, masses of them being devoted to the discharge of one function, others to that of another, and so on.
There is little wonder, then, that in a colony of protoplasts such as constitute a large plant a considerable degree of differentiation is evident, bearing upon the question of water supply.
Others are devoted to the work of carrying it to the protoplasts situated in the interior and at the extremities of the plant, a conducting system of considerable complexity being the result.
Communication between the various protoplasts of the colony is, however, carried on by means of fine protoplasmic threads, which are continuous through the cell-walls.
Instead of regarding these as only ministering to the construction of the bulky portions, the living protoplasts take the first place as the essential portion of the tree, and all the other features are important mainly as ministering to their individual well-being and to their multiplication.