The latest research proposed a new point of view about the material composition of so-called ‘humic substances,’ isolated from natural objects (soils, peats, sapropels, and composts) by alkaline solutions, and presented the conceptual model of direct influence of ‘humic substances’ on biochemical and biophysical processes into plants. ‘Humic substances’ are essentially black liquor, i.e., a product artificially obtained because of the alkaline hydrolysis of organic material from natural objects. Black liquor consists of a complex mixture of a variety of organic compounds. According to the proposed model, the biological activity of black liquor connects with accelerating the circulation of nutrients within plants, increasing the permeability of cell membranes, exhibiting de-toxicological properties, optimizing the ratio of organic and mineral anions in plants, and using some HS components as organic nutrients, inducing gene expression. Therefore, humic substances solutions have multifaceted effects on green vascular plants due to their direct influence on biochemical and biophysical processes.