Michal Simunek, Uwe Hoßfeld, and their co-editors are doing a great service to the Mendel Industry with their recent collections of primary sources. They are reopening some old questions about Mendel's life and ‘rediscovery’; raising some new ones about the Austrian, Moravian and Bohemian contexts; and providing resources for answering them.

Under review here are the volume of letters about Mendel by his nephews, Alois and Ferdinand Schindler, and the volume of correspondence between the brothers Tschermak (also known as von Tschermak-Seysenegg) – Erich, the plant breeder and co-rediscoverer of Mendel's famous paper, and Armin, the animal physiologist. An earlier volume on Mendel's reception in Moravia and Bohemia has already been reviewed in this journal ((2011) 44, pp. 611–612).

By far the more important of the volumes is The Mendelian Dioskuri, which contains letters exchanged between the Tschermaks (mostly from Armin to Erich) that will be quite new to most historians of genetics. This material should stimulate new research into Erich's role in the rediscovery and the likely influence of Armin's physiological understanding of heredity on Erich's reading of Mendel.

The title of the volume compares the duo to the mythical Castor and Pollux, but I am not sure how the comparison is intended. To me, the letters reveal more scheming careerism than epic heroism, but I suppose the sons of Zeus must have had clay feet, too. The Tschermaks were good at self-promotion and self-congratulation. We see them (or at least Armin) in April 1900, studying de Vries's and Correns's publications, and gloating about those botanists' (presumed) ignorance of Mendel. We see them planning to leverage their advantage for Erich's benefit in the ensuing competition for status as co-rediscoverers and in Erich's quest for a professorship. And for the next half-century we see them repeatedly manipulating the system – or systems, for they survived many institutional and political changes in the Austrian Empire and First Republic, Czechoslovakia and the Third Reich.

In these letters, Armin comes off as the brighter of the two stars, managing Erich's career, interpreting Mendel for him, and cautioning him against rushing to accept overly speculative conceptions of genes and genetic mechanisms or evolutionary theories. But was Erich just a passive recipient of instructions from an overbearing big brother? There is so little from Erich's side of the conversation that it is hard to judge.

Questions of credit loom large in the rediscovery literature, and these letters will allow a better reconstruction of who read Mendel when and understood it how. They should help to put Erich Tschermak onto a more equal footing with de Vries and Correns, but they will also complicate the picture by bringing Armin into it. Should we now say that Erich had a co-co-rediscoverer? And how, exactly, did he understand Mendel's principles, when reading the paper through Armin's physiological lens? Did he see the same things in it as de Vries and Correns? It has been suggested before that he did not, but rather underestimated the significance of segregation.

These letters confirm that the Tschermaks did not have much to say about segregation, but dwelt instead on the physiological potency or value (Wertigkeit) of traits. They saw Mendelian dominance and recessiveness as special cases on a continuous scale of potency. They were cautious about everything else in Mendel. Does that disqualify them as rediscoverers? The editors suggest that the Tschermaks did indeed have a distinct interpretation but that the result should be seen not as a failure to get Mendel right, but as a foundation for a distinct line of Austrian or perhaps Austro-Czech thought.

The volume of Letters on G.J. Mendel reproduces the correspondence of another pair of brothers, the Schindlers, concerning their uncle Gregor. These are the accounts they sent to William Bateson, Hugo Iltis and Erich Tschermak, in response to their first inquiries about Mendel's life. In an appendix, we also find some of the first biographical sketches of Mendel by Bateson, August Padtberg and Alois Schindler. Most of this material will be known to Mendel specialists, but it is very useful and instructive to see it all gathered in one place.

There are few first-hand accounts of Mendel, so the reminiscences of his nephews have been invaluable to biographers. Even though they were too young to have direct knowledge of Mendel's early life or scientific endeavours, they were able to supply information about his family, home town and education, as well as insight into Mendel's character and his later work at the monastery.

As the editors note, these early twentieth-century discussions are of interest not only for what they say about Mendel, but for what they reveal about the Mendelians and what most interested them about the founder of their field. The Schindlers wrote about their uncle with evident pride and wracked their brains for memories that might have shown them that Mendel was aware of being onto something big or disappointed at going unrecognized for it. There is also much about genealogy and national heritage, concern that the name Mendel might turn out to be of Jewish origin, and speculation about Mendel's views on evolution and religion.

The editors' introductions to both volumes, the sketch of Mendel's life by Bateson, and F. Schindler's letters to Bateson are in English, the rest is in German. Each volume also includes a name index, a bibliography of secondary literature and photographs.