The researchers found that the stem structure and growth pattern of ancient branch ferns were significantly different from those of living trees. In common living trees, the tissue vascular bundles that play the role of support and transportation are often a single whole. Through continuous secondary growth, it thickens the stems of trees and produces rings. In Devonian branch ferns, there are at least dozens of independent vascular bundle systems intertwined into a network. On the whole, they are cylindrical and form a three-dimensional grid system with other dredging organizations. in this grid system composed of vascular bundles, each single vascular bundle can grow thicker and produce growth rings, and at the same time, by splitting and proliferating each other, the vascular bundle system is constantly expanded to achieve the thickening of the plant as a whole.
The most suitable title for this passage is 'The long evolution of trees'.