"When the ivy has found its tower, when the delicate creeper has found its strong wall, we know how the parasite plants grow and prosper"

In this quote, Anthony Trollope uses the imagery of ivy and a tower to show the concept of parasitic plants. He suggests that when the ivy has actually found its assistance in the kind of a tower, and the fragile climber has discovered its strength in a strong wall, they have the ability to grow and flourish as parasites. This can be analyzed as a metaphor for how some people or entities might count on others for their own success and development. Trollope's usage of nature in this quote highlights the interconnectedness of living beings and the concept that in some cases, we need the support of others to reach our full potential.