These knobbly corms are Winter Aconites (Eranthis hyemalis). A few specialist nurseries like Shipton Bulbs cultivate and sell them for autumn planting. Strictly speaking a corm is a swollen but solid underground stem; a true bulb is also a modified stem but comprises layers of leaves around a bud. Bulbs and corms are storage organs of nutrients for future growth.

 Winter Aconites are an introduction from the southern Mediterranean that has naturalised here and there in the UK. For example there is a rather fine patch near Hitchin that I make a point of going to see most years. [see entry dated 16th. February 2017] 

 I would like them to naturalise in my garden but London clay doesn't suit them. However there is one spot where a few have taken -the soil seems a bit lighter there- so I'm planting some more. They are delightful in late winter/early spring so here's hoping...