Four internal factors which affect the rate of transpiration are :
1. Leaf area - If area of the leaf is more then transpiration is faster.
2. Structure of leaf - The anatomical features of leaves decide the rate of transpiration like sunken stomata, vestigial stomata, presence of cuticle and many more.
3. Root shoot ratio - The rate of transpiration is directly proportional to the root shoot ratio.
4. Age of plants - Younger plants show a lower rate of transpiration, however, when they reach the age of maturity shows faster rate of transpiration.