For this plasterer's rather than mason's work, the Horned and the Three-horned Osmia employ soft earth. This material is different from the Mason-bee's cement, which will withstand wind and weather for many years on an exposed pebble; it is a sort of dried mud, which turns to pap on the addition of a drop of water. The Mason-bee gathers her cementing-dust in the most frequented and driest portions of the road; she wets it with a saliva which, in drying, gives it the consistency of stone. The two Osmiae who are the almond-tree's early visitors are no chemists: they know nothing of the making and mixing of hydraulic mortar; they limit themselves to gathering natural soaked earth, mud in short, which they allow to dry without any special preparation on their part; and so they need deep and well-sheltered retreats, into which the rain cannot penetrate, or the work would fall to pieces. While exploiting, in friendly rivalry with the Three-horned Osmia, the galleries which the Mason-bee of the Sheds good-naturedly surrenders to both, Latreille's Osmia uses different materials for her partitions and her doors. She chews the leaves of some mucilaginous plant, some mallow perhaps, and then prepares a sort of green putty with which she builds her partitions and finally closes the entrance to the dwelling. When she settles in the spacious cells of the Masked Anthophora (Anthophora personata, ILLIG.), the entrance to the gallery, which is wide enough to admit one's finger, is closed with a voluminous plug of this vegetable paste. On the earthy banks, hardened by the sun, the home is then betrayed by the gaudy colour of the lid. It is as though the authorities had closed the door and affixed to it their great seals of green wax. So far then as their building-materials are concerned, the Osmiae whom I have been able to observe are divided into two classes: one building compartments with mud, the other with a green-tinted vegetable putty. The first section includes the Horned Osmia and the Three-horned Osmia, both so remarkable for the horny tubercles on their faces. The great reed of the south, the Arundo donax, is often used, in the country, for rough garden-shelters against the mistral or just for fences. These reeds, the ends of which are chopped off to make them all the same length, are planted perpendicularly in the earth. I have often explored them in the hope of finding Osmia-nests. My search has very seldom succeeded. The failure is easily explained. The partitions and the closing-plug of the Horned and of the Three-horned Osmia are made, as we have seen, of a sort of mud which water instantly reduces to pap. With the upright position of the reeds, the stopper of the opening would receive the rain and would become diluted; the ceilings of the storeys would fall in and the family would perish by drowning. Therefore the Osmia, who knew of these drawbacks before I did, refuses the reeds when they are placed perpendicularly.