This essay explores the historical development of the understanding that calcium (Ca²⁺) is a crucial intracellular regulator of plant growth and development. It focuses on research from the mid-1960s to the mid-1980s, highlighting key studies that established Ca²⁺ as a second messenger in plant cells. The essay discusses early studies on the role of Ca²⁺ in plant cell walls and membrane permeability, emphasizing its interaction with pectin and its influence on cell growth and development. It also examines the role of Ca²⁺ in muscle contraction in animals, which provided a foundation for understanding its regulatory functions in plant cells. The essay further explores the discovery of Ca²⁺ amplitude modulation in nonmuscle cells and its application in plant cells, including studies on cytoplasmic streaming, cell division, polarized growth, and secretion. The role of Ca²⁺ in plant growth regulators, light responses, and Ca²⁺ homeostasis, including the involvement of pumps and channels, is also discussed. The essay concludes by emphasizing the significance of Ca²⁺ as a regulator of plant development, highlighting its role in various physiological processes and its importance in maintaining cellular homeostasis.This essay explores the historical development of the understanding that calcium (Ca²⁺) is a crucial intracellular regulator of plant growth and development. It focuses on research from the mid-1960s to the mid-1980s, highlighting key studies that established Ca²⁺ as a second messenger in plant cells. The essay discusses early studies on the role of Ca²⁺ in plant cell walls and membrane permeability, emphasizing its interaction with pectin and its influence on cell growth and development. It also examines the role of Ca²⁺ in muscle contraction in animals, which provided a foundation for understanding its regulatory functions in plant cells. The essay further explores the discovery of Ca²⁺ amplitude modulation in nonmuscle cells and its application in plant cells, including studies on cytoplasmic streaming, cell division, polarized growth, and secretion. The role of Ca²⁺ in plant growth regulators, light responses, and Ca²⁺ homeostasis, including the involvement of pumps and channels, is also discussed. The essay concludes by emphasizing the significance of Ca²⁺ as a regulator of plant development, highlighting its role in various physiological processes and its importance in maintaining cellular homeostasis.