Within the first few decades of the nineteenth century, Ireland became heavily dependent on potato farming. Potatoes are nutritious and easy to grow, and they thrived in the damp soil and wet climate of the Emerald isle. Tenant farmers began to grow potatoes as the primary source of food for themselves and their families.

Then, during the summer of 1845, something strange began to happen. A magazine called The Gardener's Chronicle reported that a "blight of unusual character" was attacking potatoes. Everywhere in Ireland, potatoes began to rot and turn black. By the beginning of the twentieth century, starvation and emigration would cut the population of Ireland in half, while Ireland's principal food crop rotted in the fields.

Nutrients from decomposing potatoes enter the blight organism by diffusing through its cell walls. Which organism described in this chapter feeds in a similar way?