The conservation experiments of the previous chapters yielded results which make us wary of too simplistic an interpretation of a chronological order of acquisition. Clearly, the fact that elementary number is conserved well before continuous quantity does not mean that the latter concept is derived directly from the former. A complex system of interdependent relationships links the two notions. Con servation of length-a unidimensional continuous quantity-is usually acquired at a slightly later age than that of matter. Once again, the question of a link with the earlier conservation has to be explored. When elementary number conservation has been acquired, can the system of operations bearing on a (still restricted) number of ele ments be extended directly to the conservation of a number of elements which, when put together, form a certain “length”? Or does conservation of length also show complex relationships with earlier conservations?