The amount of DNA in an unreplicated haploid cell (the C value) is relatively constant within a species. However in higher plants it is particularly variable between species, ranging over nearly three orders of magnitude (Bennett and Smith 1976). The lowest amount recorded to date is in the ephemeral crucifer, Arabidopsis thaliana. Results from reannealing experiments originally suggested that this species has around 70000 kb per genome (Leutwiler et al. 1984), although recent data from genomic libraries have put it closer to 100000 kb. At the top of the scale lie various monocot species. For example, the true lilies (Lilium species) have around 3040 million kb per genome, while the record belongs to Fritillaria species, also bulbous monocots but with about twice the level of their Lilium relatives. Thus plant gehomes can range in size from 100000 to nearly 100000000 kb! And yet the structural and developmental complexity of pIant species with the Iowest amounts of DNA per cell is not fundamentally different from those with the highest. The number of different genes required to