Wood anatomy

introduction
ontogeny of secondary vascular tissues
growth rings
heart wood
types of heart wood
sap wood
wood parenchyma

1. Wood Anatomy Presented by ; Sumra kazbanu A . M sc sem 2 R oll no . - 2 15 CBO 405 D epartment of life sciences , H . N . G . U . Patan

2. CONTENTS Introduction Ontogeny of secondary vascular tissues , Growth Rings , Heart wood , Types of H eart wood , S a p w o o d , W o o d parenchyma

3. Introduction In most dicotyledon s and gymnosperms , t h e s t e m s increase i n g i r t h b y t h e a c t i v i t y o f l a t e r a l m e r i s t e m s . A tree stem consists of three areas; pith, xylem a nd bark. The central pith is u sually bare visible and does not increase in size through the li fe of the tree. A cylinder of wood, known scientifically as xylem ries in diameter with age and r ate of growth. And finally, the bark sheath can b e subdivided into inner bark and outer bark .

4. Ne w wood and inner bark are ad ded each year by the activity of a layer of dividing cells sandwiched between the inner bark and sapwood. New bar k production is relatively small compared with new wood production, and bark is continually being shed to the outside of the stem, thus in older trees the greatest volume of the stem is wood. Since N e w wood is added to the outside of existing w ood the oldest wood is close to the pith, and the most recent is close to the bark.

5. Ontogeny of secondary vascular tissues The initiaation of secondary vascular tissue occurs after the maturation of primary xylem and phl o e m . A t t h i s s t a g e t h e c a m b i u m i s represented by a single layer of cells . The primary tissues lying outside the secondary vascular tissues are subjected to pressure from the inside by the enlarging secondary vascular cylinder . The primary phloem is crushed and becomes non-conducting .

6. The cortex persists for a longer time as it increases in circumference by cell division and cell expansion . The epidermis may also persist throug h c e l l d i v i s i o n a n d c e l l e n l a r g e m e n t t o a c c m m o d a t e t h e d i a m e t e r increase as t h e r e s u l t o f secondary g r o w t h . H o w e v e r , i n m o s t p l a n t s w i t h c o n t i n u e d s e c o n d a r y g r o w t h t h e s e o u t e r t i s s u e s a r e c o m p l e t e l y c r u s h e d b y t h e f o r m a t i o n o f p e r d i e r m w i t h i n t h e m during secondary growth. These dead peripheral layers are eventually eliminated by de c a y o r b y a b s c i s s i o n .

7. Growth Rings The secondary xylem in the s t e m s o f p a r e n n i a l p l a n t s c o m m o n l y c o n s i s t s o f c o n c e n t r i c l a y e r s , e a c h o n e o f w h i c h represents a seasonal i n c r e m e n t . I n t r a n s v e r s e s e c t i o n o f t h e a x i s , t h e s e l a y e r s a p p e a r a s r i n g s , a n d a r e c a l l e d a n n u a l r i n g s o r g r o w t h r i n g s . Each layer represent s the grow t h o f o n e y e a r . T h e w i d t h o f growth rings varies greatly and de p e n d s u p o n t h e r a t e o f g r o w t h o f t r e e .

8. In regions with a pronounced cold season , the activity of t h e c a m b i u m t a k e s p l a c e o n l y d u r i n g t h e s p r i n g a n d s u m m e r s e a s o n s t h u s g i v i n g r i s e t o t h e g r o w t h i n d i a m e t e r o f w o o d y p l a n t s . I n s p r i n g o r s u n m e r t h e c a m b i u m i s m o r e a c t i v e a n d f o r m s a g r e a t e r n u m b e r o f v e s s e l s w i t h w i d e r c a v i t i e s . I n w i n t e r o t a u t u m n s e a s o n , h o w e v e r t h e r e i s l e s s n e e d o f v e s s e l s f o r s a p t r a n s p o r t , t h e c a m b i u m i s l e s s a c t i v e . EARLY W O O D : - T h e w o o d d e v e l o p e d i n t h e s u m m e r o r s p r i n g s e a s o n i s c a l l e d s p r i n g w o o d o r e a r l y w o o d . Early wood is inner layer of growth rings . The early w o o d z o n e s o f a g r o w t h rings typically consists of thin walled , l a r g e r d i a m e t e r c e l l s a n d a l s o a p p e a r l i g h t e r i n c o l o u r .

9. Late wood : - The wood formed in winter or autumn season is known as autumn w o o d o r l a t e w o o d . L a t e w o o d i s a o u t e r layer of growth rings . Late wood z o n e s t h i c k w a l l e d , s m a l l e r d i a m e t e r c e l l s a n d a l s o a p p e a r d a r k e r o r b r o w n s h a d e i n c o l o u r .

10. Dendrochronology : - Each annual ring corresponds to one year ' s growth , and on t h e b a s i s o f t h e s e r i n g s t h e a g e o f a p a r t i c u l a r p l a n t c a n e a s i l y b e calculated . T h e d e t e r m i n a t i o n of age of a tree by counting the annual rings , is known as dendrochronology.sometimes two annual rings are formed in a single year , a n d i n s u c h c a s e s t h e c o u n t i n g o f t h e a n n n u a l r i n g s d o e s n o t s h o w t h e c o r r e c t a g e o f t h e t r e e . t h i s h a p p e n s p e r h a p s b e c a u s e o f t h e d r o u g h t c o n d i t i o n p r e v a i l e d i n t h e m i d d l e o f a g r o w i n g .

11. Tyloses : - In many plants , the walls of the xylem vessels produce ballon like outgrowth into t h e l u m e n o f t h e vessels , are called Tyloses . Usually these structure are formed in secondary xylem . Tyloses are formed by the enlargement of t h e p i t membranes of the half border e d p i t s p r e s e n t i n b e t w e e n a p a r a n c h y m a c e l l a n d a v e s s e k o r a tracheids .

12. HEART WOOD & S A P W O O D Sap wood Heart wood The outer region of the old tree s i s s a p w o o d o r a l b u r n u m . The central region of the old tress is called heart wood or duramen . The sapwood consists of recently formed xylem elements . It is filled up with tannins , resins , gums an d o t h e r substances . It is not hard and durable . It is hard and durable . T h i s i s o f l i g h t c o l o u r a n d c o n t a i n s s o m e l i v i n g c e l l s a l s o i n t h e a s s o c i a t i o n of v s s l e s & fibres . It looks black or dark brown due to the presence of various substances in it . Generally the vessels are not plugged with tyloses . Usually the vessels remain plugged with tyloses .

13. This part of the stem performs the physiological activities , suc h a s c o n d u c t i o n o f w a t e r a n d n u t r i e n t s , storage o f f o o d e t c . . The function of heart wood is not of conduction , it gives only mechanicak support to the stem .

14. (3) Diffuse-porous hardwoods (Figure 4c). The last group of species has vessels (pores) that are uniform in size across the entire growth ring (yellow poplar, gum and maple). These vessels are usually small, uniform in size and are very difficult to see with the naked eye (a hand lens is needed

15. Types of heart woo d 1 ) Ring-porous hardwoods : - for some groups of species (oaks and elms) the earlywood/ latewood transition occurs abruptly and is very distinct. Within each growth ring, a band of large earlywood vessels (pores) is clearly visible to the naked eye, after which a band of latewood vessels appears much smaller and requires the use of a hand lens to see.

16. 2) Semi-ring-porous hardwoods : - For another group of species (black walnut, butternut and hickory) the pore transition from large to small diameter within a growth ring is gradual. The pores in the earlywood zone have a largediameter that gradually decreases in size as pores enter the latewood zone.

17. (3) Diffuse-porous h a r d w o o d s : - t h e last group of species has vessels (pores) that are uniform in size across the entire growth ring (yellow poplar, gum and maple). These vessels are usually small, uniform in size and are very difficult to see with the naked eye (a hand lens is needed ) .

18. Ring porus heart wood also divided follow types : - Solitary pores : single pores that do not touch any other pores e venly spaced across cross section (maples). Pore multiples : arrangement where two to five pores appear grouped together.Pore multiples usually occur in radial rows (cottonwood), but can occur in both radial and tangential directions (Kentucky coffeetree). Pore chains : arrangement where pore multiples appear in radial direction only. Nested pores : when larger numbers of pores contact each other both radially and tangentially (cluster). W avy bands : Pores are arranged in irregular concentric bands. Also called ulmiform because this characteristic is distinctive of all elms ( also seen in strawberry )

19. Sap wood Resin Canals : - The first step after making the determination that a wood specimen is softwood due to the absence of pores is to inspect the cross-section surface for the presence of resin canals. Resin canals are tubular passages in wood that exude pitch, or resin, to seal off wounds that occur due to insect or mechanical damage. Resin canals most often occur in or near the latewood zone of the growth rings. Softwoods can be separated into two classifications based on the presence or absence of resin canals.

20. E x a m p l e s : - Species that have resin canals include pines, spruces, larches and Douglas-fir. The species that do not have resin canals include firs, hemlocks, cedars, redwood, baldcypress and yew .

21. Woods with resin canals are further separated into two groups: (1) those with large resin canals pines, and (2) those with small resin canals D ouglas fir, spruce and larch. Using a sample wood identification set to compare the size and number of resin canals of different species is useful in determining how much they can differ between species. For example, most pines have quite large and numerous resin canals that can be seen without the aid of a hand lens.

22. Wood parenchyma Parenchyma are small, thin-walled, longitudinal cells that provide food storage. These cells are sparse in softwoods but are often quite significant in hardwoods. Parenchyma are often very small and difficult to see. However, there are many species with visible and unique arrangements of parenchyma cells that offer a clear structural feature for decisive identification.

23. There are two basic types of parenchyma: paratracheal and apotracheal . The major difference between them is that paratracheal parenchyma make contact with the pores or vessel elements, while apotracheal parenchyma are separated from pores by fibers or rays . In most species, apotracheal parenchyma are not be useful in identifying wood with just a hand lens. Paratrachal parenchyma appears in many forms, and is often more u seful for identification. For example, in hickory the banded parenchyma looks like a reticulate, Òweb-likeÓ formation as it connects between the rays and pores. This Òweb-likeÓ appearance is unique to hickory.

24. Reference s A Textbook of botany - Angiosperms By : - B .P. Pande y h t t p : / / w o o d 2 8 . f o r e s t r y . u b c . c a / f i l e s / 2012 / 08 / w o o d - a n a t o m y . h t t p : / / les.bf.uni-lj.si / fileadmin / datoteke-asistentov / kcufar / english .

25. T H A N K Y O U