The development and most significant cellular changes in the structure of the Rollinia emarginata Schlecht rays were observed from the tangential longitudinal sections of the cambium to the medulla . (Annonaceae). The characteristics of the rays of the outermost layers of the secondary xylem are described and the main changes in their structure in the different stages of secondary development are considered. The cellular changes observed are extremely variable, occurring singly or in complex combinations.
The most significant cellular changes observed during the development of the rays are the following: origin of radial initials from fusiform initials or radial initials of the exchange; changes resulting from the intrusive vortexing of the fusiform initials through a group of radical initials and the loss of radical initials of the exchange. Based on these cellular transformations, the most important changes in the origin of the secondary rays, increase and width, and reduction in the height of the multiseriate rays are considered.