(i) It indicates that the element is actively mobilised. The parts of the plant that show the deficiency symptoms also depend on the mobility of the element in the plant.
For elements that are actively mobilised within the plants and exported to young developing tissues, the deficiency symptoms tend to appear first in the older tissues.
(ii) Two elements which are highly mobile are phosphorus and sulphur and two which are relatively immobile are molybdenum and boron.
(iii) The aspect of mobility of elements is important to horticulture and agriculture.
The deficiency symptoms tend to appear first in the young tissues where the elements are . relatively immobile 'and are not transported out of the mature organs.
For example, elements like sulphur and calcium are part of the structural component of the cell and hence, are not released easily.