The meaning of the first part of the word is clear to all of us. It means many, much, or numerous, from the Greek polu. The second half of the word, ploid, is not so obvious. It means something like "of the self." Id, the operative part, was derived from the Greek idios for individual, private, or peculiar, the original meaning of idiot was a private person.

In the late nineteenth century a German geneticist used the same term as Freud used in psychology to denote what was then known as the germplasm, and what we now know as the number of sets of chromosomes. The number of sets of chromosomes is important because it controls the outcomes of sexual reproduction. Most of the organism we are familiar with have two complete sets of chromosomes. One set is inherited from each parent. Each set has all the genes for everything that makes up the organism and its life functions. That means each characteristic is controlled by two genes, each on a separate chromosome.

Multi-celled animals and higher plants are typically diploid. Diploid cells produce offspring cells with only one set of chromosomes. These cells are called "haploid" and are known to us as gametes or eggs and sperm. When a cell duplicates its chromosomes to produce two new cells, the division is not always complete, leaving a cell with more or fewer sets of chromosomes than normal. The result of two gametes combining to produce a cell with more than two sets of chromosomes is uniformly fatal in higher animals, but not in plants. For example, if a normal (haploid) gamete combines with one that didn't divide properly, and is still diploid, a triploid is produced.

Rhododendron diaprepes var. 'Garguantua' is a triploid. Its leaves and the plant in general are larger than specimens of the species itself with diploid cells. The general term for organism possessing more than the usual numbers of sets of chromosomes is polyploid.

Triploid plants will typically not reproduce successfully but, if the numbers of sets are even, sexual reproduction in higher plants can result in large numbers of sets of chromosomes. The resulting polyploids will have larger and larger body parts as the chromosome sets increase. Farmers, before we knew about polyploidy took advantage of the phenomenon to produce bigger and bigger tomatoes and other crops.

So, the next time you are buying or growing a beefsteak tomato thank the process that produces errors in cell division that give us polyploids.