de vries came to realise that the principle of randomness does not sufficiently account for this apparently infinite variation in natural phenomena. Works such as one, two and three hours beneath my apple tree (1975), under the birch (1982), beneath the maples beside the spring (1992) in which he has fixed the leaves as they have fallen in a seemingly random configuration, have made visible, says de vries, "that which people do not see any more. but [they're] also about randomness in nature, as well ... randomness and chance. in the beginning i said when a leaf falls from a tree there are many factors making the leaf at a certain moment fall on a certain point and this togetherness [of factors] i called randomness. but later i saw that everything is causal, and 'randomness' in fact expresses our inability to grasp the complexity of all these causes." (from a conversation with Paul Nesbitt, Royal Botanic Garden Edinburgh, 1992).

'chance and change' is, then, de vries's dynamic version of the evolutionary principle, accounting at once for the development of species and species variation. In this sense, works such as 72x erophila verna (1994) and 148x salix elaeagnos (1993) may be regarded as demonstrations of chance fields, for every specimen in each of the arrays - identified as of identical species (and in the case of the Salix leaves, coming from the same tree) - is different from every other, and the differences have been wrought by subtle 'changes' in their immediate situations, in what de vries calls "a complicated chance and change structure". 'chance and change' works through millennia to originate and develop species, within a single generation to create morphological and behavioural diversity, and within the single life of an organism to determine its most minute transformations. The principle also accounts for every moment's difference from every other: the opposition of the moment of stillness to the timeless flow; the cloud now billowing, now dispersing, the ripple and wave now visible, now taken up into the next turbulent surge: stasis/kinesis unending!