 I have [ ... ] reason to believe that humble @-@ bees are indispensable to the fertilisation of the <unk> ( Viola tricolor ) , for other bees do not visit this flower . From experiments which I have tried , I have found that the visits of bees , if not indispensable , are at least highly beneficial to the fertilisation of our clovers ; but humble @-@ bees alone visit the common red clover ( Trifolium <unk> ) , as other bees cannot reach the nectar . 
