1. Compensatory responses after damage were studied in two closely rel
ated annual hemiparasites of the genus Melampyrum. We followed the gro
wth and the seed set of individuals subjected to clipping of the main
stem, defoliation and removal of flowers and unripe fruits. 2. Defolia
tion resulted in decreased seed set and growth. Despite the hemiparasi
tic life-style of the species, the leaves are thus important, either f
or photosynthesis or because transpiration makes possible the acquisit
ion of resources from a host. 3. There was a trade-off between early a
nd late season reproduction: when all the flowers or unripe fruits wer
e removed in early season, the plants enhanced their seed production i
n late season, compensating totally (in Melampyrum pratense) or partia
lly (in Melampyrum sylvaticum) for the loss of the seeds from early se
ason flowers and fruits. This compensation was mainly brought about th
rough changes in the abortion regimes of reproductive structures, not
through regrowth. Thus, flower production substantially outstripped th
e ability of the plants to provision all their seeds. 4. After main st
em clipping the branches produced more fruits and seeds per flower in
M. sylvaticum and fewer in M. pratense than the branches of the contro
l plants. The timing of the damage determined the compensation mechani
sm in M. sylvaticum: plants compensated by regrowth (increased flower
number) after main stem clipping in May and by reducing seed abortion
after main step clipping in June. 5. A large part of the findings can
be accounted for in terms of resource allocation and the timing of the
damage. The different responses to main step clipping, however, sugge
st that differences in the architecture of the species are also import
ant in compensatory responses.