WOOD-ELEMENTS. 



79 



tissue just under the bark of dicotyledonous plants). Their 

 walls are thin, and at first nearly or quite free from pits or 

 other markings. 



They grade into three constantly recurring forms ; namely, 

 (1) parenchyma (see 254) ; (2) attenuated forms, often so slen- 



14 ^c=j 23 



59 



der as to deserve the name of fibres ; (3) forms with peculiar 

 markings at most points of contact, and thus much resembling 



ducts or vessels. 







FIG. 59. Drawings of wood-elements. 13. Trachei'd from Tectona grandis. 14-18. 

 Porlieria hygrometrica. 14. Conjugate substitute fibres seen in transverse section. 

 16. Ordinary substitute fibre after maceration. 17, 18. Conjugate substitute fibres 

 after maceration. 19-22. Cytisus Laburnum ; tlie elements separated by maceration. 

 19. Wood-parenchyma fibre. 20. Substitute fibre. 21. Simple Hbriform fibre. 22. Tra- 

 chei'd. 23. Cross-section through the cambium and youngest wood of Cytisus Labur- 

 num. 24-25. Ducts from Mai innia Aquifolium. 24. After maceration. 25. Longitudinal 

 section. 26-31. Ducts from Hieracium, separated by maceration ; showing the ex- 

 tremity only. 32-34. Ducts from Onorpordon acanthium, separated by maceration. 

 35. Spirally marked duct from Vitis vinifera, after maceration. 36. Libriform fibre 

 from Jatropha Manihot. (Sanio.) 



