Growth in plants occurs in two ways: primary and secondary.
Primary growth causes the plant to grow in length, both below and above the ground, due to the apical meristems that are actively dividing into these regions.
Secondary growth causes the plant to grow in width due to the presence of lateral meristems or cambium layer which actively divides to bring about this kind of growth.
Here the section is stained with Safranin(dilute) and Light green stain(dilute). For more information on staining-https://byjus.com/biology/preparation-and-study-of-transverse-section-of-dicot-and-monocot-roots-and-stems/