=Stipules=, _n._ L. _stipula_, a stalk, stem, blade; the small, leaf-like appendages at the base of the petiole of leaves. =Stoma=, _n._ From a Greek word meaning “mouth-opening”; a small opening in the skin of leaves and young stems leading to the air cavities within the plant; a breathing pore. =Stomata=, _n._ The plural of “stoma.” =Strengthening cells=, _n._ The cells with tough or hard walls that serve to give firmness and support to plant tissues. =Suction=, _n._ L. _sugere_, to suck; the process of sucking. =Sulphur=, _n._ A solid substance found in the earth’s crust in certain places; it is one of the constituents of protoplasm, and although occurring in it in very small quantities, it is essential. =Sulphuric acid=, _n._ Oil of vitriol, a combination of hydrogen, sulphur, and oxygen. Sulphuric acid is found in the earth and in the air in very small quantities, and is the source from which plants as a rule derive their sulphur. T. =Tertius=, _n._ L. _tertius_, third; the name given in this book to a suppositional plant. =Thoreau=, _n._ Henry David Thoreau, an American author of the present century, wrote a number of delightful books on nature. =Tissue=, _n._ L. _texere_, to weave; a woven fabric; the cellular fabric of plant structures. =Tropæolum=, _n._ From a Greek word meaning “a turning,” hence, a turning of the enemy, a defeat; finally, the sign of a defeat, a trophy; the name of a plant, so called because of the shield-shaped leaves, many shields together suggesting trophies taken from the enemy. =Tube cells=, _n._ The cells that build up the tubes of plants. =Tuber=, _n._ L. _tuber_, a bump, swelling; a thickened portion of an underground stem. The potato is a tuber; it stores up starch for the use of the growing plant. =Tubular corolla=, _n._ A tube-shaped corolla. The red honeysuckle has a tubular corolla. =Tunic=, _n._ L. _tunica_, a tunic; the name of a garment worn by the Romans; a loose flowing robe; hence, any garment; a name given to the scaly coverings of bulbs like the onion and hyacinth. =Tunicated=, _a._ Having a tunic. U. =Underground stems=, _n._ Stems that grow beneath the surface of the earth and look more or less like roots. They can always be distinguished from roots by the presence of nodes. V. =Variegated=, _a._ L. _varius_, various, _agere_, to make; marked with different colors. =Veins=, _n._ L. _vena_, a blood vessel; the blood vessels or channels through which the blood flows to the heart; the stiff, thread-like tubes forming the framework of leaves, petals, sepals, etc. =Vine=, _n._ L. _vinea_, a grape vine; a plant with a stem too long and flexible to stand alone. W.