Tree

===Buds and growth===
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[[File:Illustration Quercus robur0.jpg|thumb|upright|Buds, leaves, flowers and fruit of oak (''[[Quercus robur]]'')]]
[[File:Illustration Abies alba0.jpg|thumb|upright|Buds, leaves and reproductive structures of white fir (''[[Abies alba]]'')]]
[[File:Cycas circinalis(draw).jpg|thumb|upright|Form, leaves and reproductive structures of queen sago (''[[Cycas circinalis]]'')]]
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{{main|Bud}}

[[File:Magnolia Bud.jpg|thumb|left|Dormant ''[[Magnolia]]'' bud]]
Trees do not usually grow continuously throughout the year but mostly have spurts of active expansion followed by periods of rest. This pattern of growth is related to climatic conditions; growth normally ceases when conditions are either too cold or too dry. In readiness for the inactive period, trees form [[bud]]s to protect the [[meristem]], the zone of active growth. Before the period of dormancy, the last few leaves produced at the tip of a twig form scales. These are thick, small and closely wrapped and enclose the growing point in a waterproof sheath. Inside this bud there is a rudimentary stalk and neatly folded miniature leaves, ready to expand when the next growing season arrives. Buds also form in the [[axil]]s of the leaves ready to produce new side shoots. A few trees, such as the [[eucalyptus]], have "naked buds" with no protective scales and some conifers, such as the [[Chamaecyparis lawsoniana|Lawson's cypress]], have no buds but instead have little pockets of meristem concealed among the scale-like leaves.<ref name=buds>{{cite book |title=The World Encyclopedia of Trees |last=Russell |first=Tony |author2=Cutler, Catherine |year=2003 |publisher=Lorenz Books |isbn=978-0-7548-1292-0 |pages=[https://archive.org/details/isbn_9780754812920/page/18 18–19] |url=https://archive.org/details/isbn_9780754812920/page/18 }}</ref>

When growing conditions improve, such as the arrival of warmer weather and the longer days associated with spring in temperate regions, growth starts again. The expanding shoot pushes its way out, shedding the scales in the process. These leave behind scars on the surface of the twig. The whole year's growth may take place in just a few weeks. The new stem is unlignified at first and may be green and downy. The Arecaceae (palms) have their leaves spirally arranged on an unbranched trunk.<ref name=buds/> In some tree species in temperate climates, a second spurt of growth, a [[Lammas growth]] may occur which is believed to be a strategy to compensate for loss of early foliage to insect predators.<ref>{{cite journal |journal=Journal of Experimental Botany |volume=54 |issue=389 |pages=1797–1799 |date=August 2003 |doi=10.1093/jxb/erg225 |title=August-learning about summer |last1=Battey |first1=N. H. |pmid=12869517|doi-access=free }}</ref>

Primary growth is the elongation of the stems and roots. Secondary growth consists of a progressive thickening and strengthening of the tissues as the outer layer of the epidermis is converted into bark and the cambium layer creates new phloem and xylem cells. The bark is inelastic.<ref>{{cite book |title=Biology |last=Campbell |first=Neil A. |author2=Reece, Jane B. |year=2002 |publisher=Pearson Education |isbn=978-0-201-75054-6 |pages=729–730|edition=6th }}</ref> Eventually the growth of a tree slows down and stops and it gets no taller. If damage occurs the tree may in time become hollow.<ref>{{cite book |title=The World Encyclopedia of Trees |last=Russell |first=Tony |author2=Cutler, Catherine |year=2003 |publisher=Lorenz Books |isbn=978-0-7548-1292-0 |pages=[https://archive.org/details/isbn_9780754812920/page/16 16, 27] |url=https://archive.org/details/isbn_9780754812920/page/16 }}</ref>