
THE STEM 159 
obliquely and a vertical cleft is made in each. Stock and scion are 
then fitted into each other so that the cambiums are in contact. 
They are then tied together and the junction is sealed with wax. 
GROW TH 
The growth of a plant is usually accompanied by the addition 
of new material, but growth may consist in the rearrangement 
of materials already present. The latter is evidently the case 
when a potato or an onion sprouts in a dry, dark place, as under 
these conditions it is impossible for a plant to absorb water or 
mineral matter or to carry on photosynthesis. Growth in such 
cases 1s accompanied by an actual loss in weight, due to the 
breaking down of compounds in the process of respiration. This 
is necessary for the release of the energy used in the rearrangement 
of the materials taking part in the new growth. 
Grand period of growth. If the formation and growth of a 
plant organ or a limited part of a plant are considered, it will 
be found that during its formation the rate of growth is slow. 
As it becomes older it grows more rapidly up to a certain period, 
and then more and more slowly until it is mature and growth 
ends. The total growing period is known as the grand period of 
growth. Tt can be divided arbitrarily into three stages, or phases, 
which necessarily overlap. The first is the phase of formation, 
during which the organ or other limited part of the plant has 
its initiation. The chief activity during this period consists in 
the multiplication of cells, and the rate of growth is relatively 
slow. Before the cells have ceased to divide, the part concerned 
enters into the next phase, that of enlargement, during which 
the cells enlarge and approach their mature size. This enlarge- 
ment takes place with relative rapidity, and any part of a plant 
makes its most rapid growth while in this phase. After the cells 
have reached approximately their mature size, they enter the 
phase of maturation, during which they assume their mature 
characteristics. A part of a plant in this phase grows slowly, as 
the cells have, to a great extent, ceased enlarging. 

