->the primary developmental state of the stem axil is maintained throughout the life of many short-lived dicots and almost all monocots

e.g. field-chickweed (dicot), black nightshade (dicot), yellow star of Bethlehem (monocot)

-since plants compete for light, being taller brings massive advantages

-however the height growth with constant shoot diameter is limited

->vascular tissue can only supply a limited amount of leaves, roots, shoots

->mechanical stability limits the growth especially in height

Solution: secondary thickness growth

-enlargement of the vascular tissue and therefore higher transport capacity

-more leaves can be exposed to light and supplied

-the necesarry mechanical stability from greater diameter of lignified vascular tissue

-growth in height is possible

Disadvantage: large investment of recourses in unproductive stem (does not directly contribute to photosynthesis or seed production)

->periderm as a secondary dermal tissue replaces the epidermis

->it is impregnated with various antimicrobial substances (tannis) to protect against pests and pathogens

->the tick cork layer also protects against water loss, extreme temperature and mechanical damage

->in most woody plants, successive periderm layers are formed in the living bark (secondary pholem)