[Carl Correns' experiments with Pisum, 1896-1899]

The circumstances under which classical genetics became established at the turn of the nineteenth century have become an integral part of the standard narrative on the history of genetics. Yet, despite considerable scholarly efforts, it has remained a matter of debate how exactly the so-called 'rediscovery' of Mendel's laws came about around 1900. In this situation, unpublished research records can be invaluable tools to arrive at a more substantial and more satisfying picture of the order of historical events. This paper makes extended use of the research protocols covering Carl Correns' hybridisation experiments with Pisum sativum between 1896 and 1899. The resulting reconstruction sketches the portrait of a scientist following a particular research question--xenia--struggling with his experimental material, and slowly building up an epistemic regime in which questions and observations could acquire a relevance which did not strike Correns when he first took note of them. The microhistorical gaze through the magnifying glass of research notes reveals the kind of delays that appear to be constitutive for empirically-driven thinking in general. The research notes of Correns help not only to make this point, they also display some of the intricacies and material peculiarities which characterise the experimental process of hybridisation and the particular type of inferences it allows one to make.