In order to protect plants from frost many foam coating techniques and compositions have been devised, for example see U.S. Pat. Nos. 2,875,555; 3,555,727; 3,891,571; and 4,086,331. While useful for their intended purpose, foams are detrimental in imparting drought resistance to plants at high temperatures and in bright sun light, because the foams allow radiant heat to enter the plant but insulate the plant against the removal of heat. Other methods of protecting introduction of polyvinylpyrrolidone compositions or oil into the plant cell, for examples see U.S. Pat. Nos. 2,961,798; 3,045,394; and 4,219,965. The 965 patent also discusses transpiration of water. Transpiration control however requires penetration into the plant tissue. One disadvantage of introducing foreign substances into plant cells is the possibility that the foreign substances may enter the human food chain. Along the same lines, U.S. Pat. No. 3,399,990 discloses a method of closing plant stomata with alkenyl succinic acids. Other methods of protecting plants against drying out include coating the plants with materials that absorb and hold water, see U.S. Pat. Nos. 2,720,726 and 3,157,964. One possible disadvantage of using a water absorbing material to coat a plant is that after drying the coating material may draw moisture from the plant. The 964 patent discloses a second plastic moisture barrier which substantially prevents dehydration. Preventing a plant from transpiring water and or carbon dioxide could also lead to problems. Other U.S. Patents which disclose controlling plant transpiration include U.S. Pat. Nos. 3,791,839; 3,826,671; and 3,847,64. U.S. Pat. No. 3,611,635 discloses coating tobacco leaves by spraying the plants with a material, primarily alcohol or wax to reduce the nicotine content of the plant.
USPTO Backgrounds
USPTO Backgrounds