In Johan Otto Hagströmís Hagström, Johan Otto
(1716-1792). Swedish. Physician and
naturalist. Linnaeusís student. Linnaeus
wrote the introduction to his Pan
apum (1768), on bee-pollinated
flowers. He was one of the tutors of
Carl Linnaeus the Younger. Correspondent
of Linnaeus. letter [Hagström to Linnaeus 5 June 1763Letter L3271] to Linnaeus he had mentioned his experiments with plants that were readily eaten by rabbits and hares. In that context he had mentioned that rabbits mate when they are 9 or 12 weeks old; however, he has now found that this early mating is without effect so, at present, Hagström does not know the age of rabbits when they first mate and give birth to young. Nonetheless, writes Hagström, it is fully clear that the mother rabbit, within an hour of giving birth, mates again with the adult rabbits, as he has observed several times during the summer. The young that were born on April 22nd this year still have not given birth to young. The rabbit is pregnant for thirty days, this is certain, and if one includes the day she gives birth when she certainly mates again, then 31 days can be said to be the length of her pregnancy. Both rabbits and hares readily eat leaves and the green bark of the common willow, Salix fragilis, much more readily than leaves of aspen, which they nonetheless eat quite contentedly. It is, however, remarkable that hares do not eat sweet-gale, Myrica gale, whereas rabbits eat its leaves. Hagström has noted that leaves of the maple are very popular food for both rabbits and hares. When he was a child he knew simply that aspen leaves and cabbage leaves were food for hares.