The researchers found that compared with living trees, the stem structure and growth methods of ancient branches and ferns are significantly different. Among common living trees, the tissue vascular bundles that play a supporting and transporting role often appear as a single whole. It continuously thickens the stems of trees and produces annual rings through continuous secondary growth. In the Devonian era, there are at least dozens of vascular bundle systems that are independent and intertwined into a network. It is generally cylindrical, and forms a three-dimensional grid system with other grooming issues. In this grid system consisting of vascular bundles, every single vascular bundle can grow thickly, generating growth wheels, and at the same time splitting each other , Proliferation, and continuously expand the vascular bundle system, so as to achieve the overall thickening of the plant. The most suitable for this text title is:. ['Demystifying how ancient plants grew.', 'The long evolutionary process of trees.', 'Teach you how to look at the age of trees.', 'Identifying Branch Ferns at a Glance.']