Populus: A plant genus of the family SALICACEAE. Balm of Gilead is a common name used for P. candicans, or P. gileadensis, or P. jackii, and sometimes also used for ABIES BALSAMEA or for COMMIPHORA.Salicaceae: A plant family of the order Salicales, subclass Dilleniidae, class Magnoliopsida. The leaves are alternate and simple. Staminate (male) flowers consist of from one to many stamens. Pistillate (female) flowers consist of a one-chambered ovary with several to many ovules (potential silky seeds).Wood: A product of hard secondary xylem composed of CELLULOSE, hemicellulose, and LIGNANS, that is under the bark of trees and shrubs. It is used in construction and as a source of CHARCOAL and many other products.Trees: Woody, usually tall, perennial higher plants (Angiosperms, Gymnosperms, and some Pterophyta) having usually a main stem and numerous branches.Xylem: Plant tissue that carries water up the root and stem. Xylem cell walls derive most of their strength from LIGNIN. The vessels are similar to PHLOEM sieve tubes but lack companion cells and do not have perforated sides and pores.Plant Stems: Parts of plants that usually grow vertically upwards towards the light and support the leaves, buds, and reproductive structures. (From Concise Dictionary of Biology, 1990)Genes, Plant: The functional hereditary units of PLANTS.Lignin: The most abundant natural aromatic organic polymer found in all vascular plants. Lignin together with cellulose and hemicellulose are the major cell wall components of the fibers of all wood and grass species. Lignin is composed of coniferyl, p-coumaryl, and sinapyl alcohols in varying ratios in different plant species. (From Merck Index, 11th ed)Plant Leaves: Expanded structures, usually green, of vascular plants, characteristically consisting of a bladelike expansion attached to a stem, and functioning as the principal organ of photosynthesis and transpiration. (American Heritage Dictionary, 2d ed)Genome, Plant: The genetic complement of a plant (PLANTS) as represented in its DNA.Gene Expression Regulation, Plant: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action in plants.Plant Proteins: Proteins found in plants (flowers, herbs, shrubs, trees, etc.). The concept does not include proteins found in vegetables for which VEGETABLE PROTEINS is available.Pentanes: Five-carbon saturated hydrocarbon group of the methane series. Include isomers and derivatives.Cambium: A layer of living cells between the bark and hardwood that each year produces additional wood and bark cells, forming concentric growth rings.Droughts: Prolonged dry periods in natural climate cycle. They are slow-onset phenomena caused by rainfall deficit combined with other predisposing factors.Laccaria: A genus of white-spored mushrooms in the family Tricholomataceae. They form symbiotic partnerships (MYCORRHIZAE) with trees.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.Salix: A plant genus of the family SALICACEAE. Members contain salicin, which yields SALICYLIC ACID.RNA, Plant: Ribonucleic acid in plants having regulatory and catalytic roles as well as involvement in protein synthesis.Plants, Genetically Modified: PLANTS, or their progeny, whose GENOME has been altered by GENETIC ENGINEERING.Mesophyll Cells: Large and highly vacuolated cells possessing many chloroplasts occuring in the interior cross-section of leaves, juxtaposed between the epidermal layers.