Final answer:
If growth in the plant kingdom occurred only through lateral meristems, plants would not be able to grow in length, resulting in limited vertical development. The diversity and structure of plants would be greatly affected, with many herbaceous plants potentially unable to survive due to their reliance on primary growth for accessing light and space.
Step-by-step explanation:
If plant growth occurred only in lateral meristems, the plant kingdom would see significant changes. Primarily, plants would be unable to increase in length, as this function is attributed to the apical meristems, which promote growth through elongation of stems and roots. Instead, plants would only grow in thickness or girth, as lateral meristems like the vascular cambium and the cork cambium are responsible for secondary growth, which includes the radial expansion of plant tissue. Lateral meristems are essential for the process of increasing the girth of stems and roots during secondary growth. The vascular cambium contributes to most of the increase in girth, while the cork cambium generates a new protective 'skin' called the periderm. Without apical meristems, which are located at the tips of stems and roots, a plant's potential for vertical growth and reaching new resources would be severely limited, affecting the overall diversity and structure of the plant kingdom. For instance, trees would not be able to reach great heights and would resemble more of shrub-like structures with extensive radial growth.