I'll write some entries about bulbs too since I said on Tuesday that I'll write about seeds. Bulbs are another topic that will need a few posts to get to grips with.
 A seed is a plant in embryonic form but a bulb is a plant that's already up and running. Bulbs are bulbous because they're food storage organs. That's why bulbs are sometimes already growing in the packet when purchased- like this Crocus angustifolius that I'm potting up to grow on a window sill. The bulb already has the food it needs to start growing having assimilated it through the foliage and roots last spring.
 Bulbs then go dormant which is why they can be lifted, stored and distributed for sale. Having said that some bulbs e.g. Crocuses respond well to drying out during this process but others like Snowdrops do not. Most Galanthus species for example need to be sourced freshly lifted or planted "in the green" i.e. when they are in leaf in late winter. A dried up Snowdrop bulb is probably dead rather than dormant.
 A bulb is actually a stem with scales (modified leaves) that form around it. In fact I should be more specific and say that Snowdrops are a bulb whereas Crocuses are a corm- a swollen, underground base of a stem and like true bulbs a food storage organ. Corms are generically referred to as "bulbs" as are some tubers (the swollen ends of a stem) and rhizomes (stems that grow horizontally just above or below the surface). In bulb catalogues you will find Cyclamens which are tubers and Lily of the Valley which are rhizomes.