The length of bamboo grows much faster than that of thickness why?​

Using a slow- and fast-growing variant of bamboo, Wei and colleagues looked at cell division, growth, and gene expression (through transcriptomics, which measures all the genes being expressed by an individual) to discover which genes may be responsible for fast growth in bamboo. They found that the slow-growing variant had reduced expression of genes relating to cell wall construction, the plant hormone auxin (important for cell growth and cell division), and had irregular cell growth and cell walls. Wei and colleagues suggest that a reduced ability to produce and perceive auxin, combined with a weakened cell wall, are responsible for the slow growth seen in the bamboo variant.