president’s address. 
001 
the thicket. These various devices counteract the force of gravity 
which otherwise would keep them upon the ground. The results 
of a stimulus are often not manifest for some time. In a growing 
stem, branches extend out at all angles from the trunk, and from 
each other, and under the stimulus of light tend outwards and 
upwards. For a certain length a branch or twig may have 
a downward (geotropic) curve, due to the stimulus of gravity, 
whilst another will show an upward (heliotropic) one. These two 
curves later on may be replaced by opposite ones. Now, although 
the trend of the branches is towards the light, gravity is always 
acting as a regulating force, and pulling in opposition to the sunlight 
force, thus fixing the required position. At the same time, 
according to the necessities of the plant, these various curves are 
fixed by a thicker deposit of wood taking place on the upper or 
lower surface of the branch. Various stimuli play their part in 
causing the different curvatures. A physiological alteration in cell 
development may take place, induced by some chemical stimulus, 
at the growing point of the shoot, which will cause the shoot to 
start at a different angle. The opening of the bud may be checked 
by stimulus of cold, or it may be excited by that of light and heat, 
although all will not be affected in the same degree. A scarcity of 
water at the root may act as a stimulus, and response to this will 
be sympathetically conveyed to the growing points. By these 
various stimuli always at work, but ever varying as to time and 
action, the tree or shrub is developed, according to a fixed standard 
of form, that has its physiological value in the inherent nature of 
the plant. 
It is by no haphazard coincidence that some branches and twigs 
bend in one direction and some in another. As they sway about, 
the plant acting under the stimulus of the motion, keeps a watchful 
eye over those parts that require special stiffening. According to 
the vital necessities from within, it co-ordinates and brings under 
subjection and into their proper places all the branches and twigs 
until a perfect and harmonious whole is established. 
VOL VII. 
R R 
