growing plant to correspond with the altered
conditions of growth. The actual means by which certain buds are stimulated
into growth while others remain dormant, or are inhibited from growing, are
as yet unknown. Two theories have been advanced. One is that the growing
buds absorb all available nutrition and the others remain dormant by reason
of lack of growth-promoting material. The other is that the vegetating
(growing) tissue elaborates and sends to other parts of the organism one or
more substances, which actually inhibit growth of the other parts, as
dormant buds, etc. The experimental evidence which has been presented thus
far is inconclusive, but seems to favor the distribution of nutritional
material as the governing factor, although there is some evidence which
seems to indicate that a supposed growth-inhibiting substance is actually
translocated from rapidly-vegetating tissues to other parts of the plant.
There is, however, no explanation of how the buds, or other tissues, which
do grow get their initial stimulus, while the dormant buds do not. After
growth has once started, the changes in osmotic pressure due to the
accumulation and translocation of synthetized materials can account for the
movement of new nutritional material for the synthetic processes into the
growing organ; but this would not account for the selective stimulation of
only a part of the buds, or possible growing points, of a plant, or for an
adaptational development of others under altered conditions of growth.

The form of morphological adaptation which has been discovered in the
course of the study of the native vegetation of the campos of Brazil (which
have a very dry season and have been regularly burned over by the natives
for many generations) in which the papilionaceous shrubs have developed
underground trunks, or stems, and seem actually to profit in luxuriance of
growth when the rainy season comes on by reason of this morphological
adaptation to the unusual environmental conditions, is wholly inexplicable
by any present knowledge of the science of plant growth.

PHYSIOLOGICAL ADAPTATIONS

The type of adjustment to environmental conditions which does not result in
any recognizable alteration in the structure of the plant, but simply
permits it to grow under new conditions, manifests itself in many ways.
These adjustments are usually associated with differences in temperature
during the growing season, an