Herbo - plantologist and agronomist. He studied in America and received a diploma in Physics and Natural Science. Upon his return to Greece he took over the direction of the Zografou estate and was later appointed professor of Natural History in a high school of Athens (1879 - 1880) From1880 to 1894 he served as inspector of Agriculture at the Ministry of Interior as well as director of the Public School of Forestry and Agriculture of Athens. In 1895 he was appointed inspector of Agriculture in Cyprus and later on, when he came back to Greece he was given a post in the Ministry of Interior. He published the following; the magazine "Report on Greek Agriculture" in 12 tomes (1885 - 1896), the "Phytological Encyclopedia", "Report on the Agriculture of Cyprus" in 3 tomes, "Oak products", "Aviculture", "Agricultural products", and various other studies and theses.

Panayiotis Gennadius was a member of the French Entomological Society. During this lifetime he studied 6 new species of insects from Greece, Cyprus and Turkey (1881, 1883, and 1895).

Among the species he described in 1883 was Monophlebus hellenicus, known to us as Marchalina Hellenica. (Gennadius, 1883)