48 TRANSMISSION OF STIMULI. 
such an intercourse must of necessity be presumed to exist. When one. considers 
the unanimous co-operation of protoplasts living together as a colony, and observes 
how neighbouring individuals, though produced from one and the same mother-cell, 
yet exercise different functions according to their position; and, further, how uni- 
versally there is the division of labour most conducive to the well-being of the whole 
community, it is not easy to deny to a society, which works so harmoniously, the 
possession of unity of organization. The individual members of the colony must 
have community of feeling and a mutual understanding, and stimuli must be pro- 
pagated from one part to another. No more obvious explanation offers than that 
the protoplasmic filaments, which run like telegraph-wires through the narrow 
pores and canals in the cell-walls (see fig. 10°), serve to propagate and transmit 
stimuli from one protoplast to another. These threads of protoplasm may indeed 
be likened to nerves which convey impulses determining definite actions from cell 
to cell. 
Imagination takes us further still, and raises the cell-nucleus to the position 
of the dominant organ of the cell-body. For the nucleus not only determines 
the activity of the individual protoplast within its own cavity, but continues in 
sympathetic communion with its neighbour by means of all the threads and liga- 
ments which converge upon ıt. This last idea in particular derives support from 
indications that the filaments uniting neighbouring protoplasts have their origin 
in specific transformations in the substance of the nucleus itself. When a proto- 
plast living in a cell-cavity is about to divide into two, the process resulting in 
division is as follows:—The nucleus places itself in the middle of its cell, and at 
first characteristic lines and streaks appear in its substance, making it look like 
a ball made up of threads and little rods pressed together. These threads gradu- 
ally arrange themselves in positions corresponding to the meridian lines upon a 
globe; but, at the place where on a globe the equator would lie, there then occurs 
suddenly a cleavage of the nucleus—a partition-wall of cellulose is interposed in 
the gap, and from a single cell we now have produced a pair of cells. In this 
way, from the nucleus, and from the protoplast of which the nucleus is the centre, 
two protoplasts have been produced, each having a nucleus of its own, and they 
thenceforth live side by side, each in its own chamber. It has been proved that 
in this process of division the substance of the nucleus is not completely sundered 
by the partition as it grows, but that, as we have already mentioned, minute 
pores are kept open in the cellulose wall, and that the pair of protoplasts continue 
joined together by threads running through these pores. 
When we realize that every plant was once only a single minute lump of 
protoplasm, inasmuch as the biggest tree, like the smallest moss, has its origin 
in the protoplasm of an egg-cell or a spore; and when we consider how, by growth 
and repeated bipartition, thousands of cells are evolved, step by step, from a 
single one, whilst their protoplastie bodies still remain united by fine filaments, 
we arrive of necessity at the conclusion that the whole mass of protoplasm, living 
in all the myriads of cells whose aggregation constitutes a tree, really is, and 
