Hugo de Vries, Carl Correns, and Erich von Tschermak-Seysenegg explain the laws of heredity, and Theodor Schwann introduces cellular microscope discoveries.

Hello, I'm Hugo de Vries. Working with flowering plants, I worked out the laws of heredity. Hello, I'm Carl Correns. Using maize and peas, I worked out the laws of heredity. Hello, I'm Erich von Tschermak-Seysenegg. As a graduate student, I worked out the laws of heredity using peas. We all thought we discovered something new about how traits are inherited when we published our results in 1900. Imagine our surprise when we realized that we were "rediscovering" Herr Gregor Mendel's work from 1865. Of course these results were easier for our generation to accept because of the cellular discoveries made under the microscope. Hello, I'm Theodor Schwann. I can tell you about the cellular discoveries made under the microscope. Robert Hooke was the first to look at cork under the microscope in 1665. He was very shy, so there are no pictures of him. I'll show you what he did. Using a microscope of his own design, he saw box-like pores in the cork. Mr. Hooke called these "cells." Mr. Hooke saw cells not only in cork, but in other plants as well. He found that cells from living plants are filled with "juices." Cells from dead plants are empty of everything but air. This, of course, solved the riddle of why cork and other woods float. Since Mr. Hooke's discovery, many people looked through microscopes. Here are some of my drawings published in 1839. I defined a "cell" not by shape or size, but by the presence of a dark staining body — nucleus — found within. ONION CELLS NUCLEUS FISH NOTOCHORD CELLS FROG CARTILAGE CELLS TADPOLE CARTILAGE CELLS FETAL PIG MUSCLE CELLS PIG EMBRYO CELLS Over time, scientists observed cells with nuclei in every living organism. By the 1870's, we saw that sometimes the granular nucleus was replaced by distinctive curved fibers; these were later called chromosomes. It soon became obvious that cells from different species have different amounts of chromosomes. We began to think that chromosomes may carry the units of heredity. SALAMANDER CELL WITH CHROMOSOMES MEAL WORM CELL WITH CHROMOSOMES

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