Read it through once

Such poisonous orders should of course be avoided, but much more dangerous are those deadly plants which appear as it were accidentally in orders which are amongst the most useful friends of man. Amongst the grasses there is the deadly Darnel (_Lolium temulentum_), a first cousin and not very unlike the very commonest and one of the most useful grasses--Rye Grass (_Lolium perenne_).