The paper begins with a review of the phytohormone (plant hormone) concept vs the sense of the mammalian hormones. The term "plant growth regulators" including new naturally occurring substances is discussed in regard to their effects on both growth and development processes, and possible different mechanisms of action in two different physiological directions. Mutual interactions between auxins, cytokinins, ethylene and polyamines are examined in several growth and development processes, showing the complexity of approach of the hormonal actions in plants . The indissociability of some hormonal relationships, and their obligatory integration with primary biochemical pathways is finally shown.