Nägeli, Karl Wilhelm (1817-1891), a Swiss botanist, is remembered both for his contributions to the understanding of plant cells and for his rejection of Gregor Johann Mendel's laws of heredity. He was one of the best-known plant authorities of his time.

Nägeli was trained by German nature-philosopher Lorenz Oken. He then studied botany at universities in Geneva and Jena. In 1842, he published a paper accurately describing cell division and pollen formation by seed and flowering plants. The threadlike bodies he called "transitory cytoblasts" were later identified as chromosomes. He also discovered the function of several plant parts, including the antheridia (male reproductive structures) of ferns and the spermatozoids (motile male gametes) produced in them.

Nägeli was the first to use the botanical term meristem, which refers to the undifferentiated, growing, actively dividing cells of embryonic plant tissue. Although he gave the first accurate account of apical cells, where longitudinal growth originates, he mistakenly believed they were the main site of meristematic growth in all plants. In 1858, he showed how important the sequence of events in cell division was in determining the form of plant parts. His study of different forms of starch led him to introduce the micella, a hypothetical structural unit, which became the basis for interpretation of starch grain structure.

Nägeli was one of the first to differentiate the plant cell wall from the cytoplasm and nucleus, which in 1846 German botanist Hugo von Mohl called protoplasm. On the basis of his own chemical analyses, Nägeli showed that protoplasm contained nitrogenous material. He believed that part of the protoplasm, which he named idioplasm, was the source of a cell's hereditary character.

In the 1860's, clinging to his own erroneous beliefs about species variation, Nägeli rejected the research findings that Mendel sent him. Being rebuffed by the most distinguished botanist in Europe was one of the reasons Mendel refrained from publishing data on his late experiments and observations. Nearly 40 years passed before Mendel's laws of heredity were rediscovered and verified.