A Journey into of the Universe of in vitro Cultures of Plants. Callogenesis

After presenting a brief history of the discovery of this system of cultivation of plant tissues and cells, of the evolution in time of knowledge in this field, of the pathways of in vitro morphogenesis in plants, the paper focuses on in vitro callogenesis in plants. There are presented the types of callus that can be generated via in vitro culture (illustrated with aspects from the author's experience), the influence of factors related to the biological nature of the explants, the composition of the nutrient medium, the cultivation conditions, etc., upon some characteristics of the callus obtained. A special chapter is dedicated to the importance of in vitro cultures of callus in plants.