When poison-ivy becomes mixed in with other vines it is quite difficult to detect except by one who has carefully trained himself in observing and recognizing the plant. Also, some other vines and young plants resemble poison-ivy in many respects. The Virginia creeper and some forms of the Boston ivy are often confused with it. The Virginia creeper can always be recognized by its five leaflets radiating from one point of attachment, as compared with the three leaflets of poison-ivy arranged in the same manner. The Boston ivy with three leaflets is sometimes difficult to detect; however, as a rule not all the leaves on the plant will be divided into three leaflets. By studying a large number of the leaves it is usually possible to detect on every Boston ivy plant some leaves that have only one deeply lobed blade or leaflet, while the poison-ivy always has the three leaflets. A number of other plants are easily confused with poison-ivy. No specific rule can be observed that will easily rule out all possibility of confusion. The best policy is to learn through practiced observation to know poison-ivy on sight and then to make the determination from observation of all parts of the plant, and never to judge from a single leaf or part. _Figure 6._--Leaves of common poison-ivy, about half natural size. These may occur on the same or different plants: _A_, _B_, _C_ and _F_, less common; _D_, with even margins, the most common and generally recognized form; _E_, with lobed margins, nearly nearly as often seen as the shape in _D_. _Figure 7._--Common poison-ivy vine with clusters of flowers in the axis of each leaf. Common poison-ivy in full sunlight along fence rows or in open fields grows more in the form of a shrub than a vine. In some localities the common form is a low-growing shrub from 6 to 30 inches in height. This form, as well as the vining type, usually has a rather extensive horizontal system of rootstocks or stems at or just below the ground level. The vining form under some conditions later becomes a shrub. Plants of this type are shown in figure 5, where the vine, supported on the fence, has extended upright stems that are shrublike. In some localities the growth form over a wide range is consistently either a vine or a shrub type, while in others what seems to be the same species may produce either vines or shrubs.