Among Kaul's natural scientist friends were Frank Hawking, a British biologist and physician and Stephen Hawking's father; Sir Edward James Salisbury, a British botanist and ecologist; Ronald Melville, a British botanist; Arthur John Cronquist, an American botanist; Birbal Sahni, an Indian palaeobotanist; G.C. Mitra, an Indian botanist; Alexandr Innokentevich Tolmatchew, a Soviet botanist; Kiril Bratanov, a Bulgarian biologist; Ronald Pearson Tripp, a British palaeontologist; and René Dumont, a French agronomist.