Collections of living organisms are reservoirs of biological knowledge that operate across times and places. From the mid-20th century, scientific institutions dedicated to the cultivation of such collections have routinized and professionalized their care. But “care,” for these collections, is focused not just on individual organisms—instead, a principal aim of a curator is to maintain the integrity of a reproducing “strain,” “variety,” “line,” or “stock,” and the composition of a collection as a whole. This paper explores the forms, the material (...) dimensions, the temporalities, and the values of that care, to recover the conditions under which scientist-custodians maintain continuity of research over many decades. This paper does so by focusing on two rather different kinds of scientific collection: that of Drosophila fruit flies on the one hand, and plant seeds on the other. Their comparison is valuable because their vastly different needs and life cycles engender very different practices of care. Comparing the materialities, life cycles, needs, and values of these divergent collections helps to draw attention to the routine and the apparently mundane. First, the paper asks: what kinds of work go into managing such collections—that is, the day-to-day management and cultivation, surveillance, and administration of information? Second, it asks: how do these practices maintain the integrity of the strains and stocks, and the collections themselves? What kinds of value does this work create? Third, what are the future imaginaries that are rhetorically drawn into the funding strategies of these collections, and how do they envision future use, ownership, and control? (shrink)