Lichtenstein has established the fact that from the egg of the Aphis of Pistachio galls, Anopleura lentisci, is hatched an apterous insect (the gall-founder), which gives birth to young Aphides (emigrants), and that these, having acquired wings, fly to the roots of certain grasses (Bromus sterilis and Hordeum vulgare), and by budding underground give rise to several generations of apterous insects, whence finally comes a winged brood (the pupifera).
Of the best hay and pasture grasses, Agropyrum Elymus, Stipa, Bromus, Agrostis, Calamagrostes and Poa, there are 59 species.
Austrian brome grass (Bromus inermis) and western rye grass (Agropyrum tenerum) are both extensively grown for hay in the North-West Provinces.
A similar specialization has been observed by Marshall Ward in the Puccinia parasitic on species of Bromus, and by Neger, Marchal and especially Salmon in the Erysiphaceae.
In the last-named family the single morphological species Erysiphe graminis is found growing on the cereals, barley, oat, wheat, rye and a number of wild grasses (such as Poa, Bromus, Dactylis).