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. 



The}- grade into three constantly recurring forms ; namely, 

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



14 



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. TracheTd from Tectona grandis. 14-18. 

 Porlieria hygronietrica. 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 ; the elements separated by maceration. 

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

 cheTd. 23. Cross-section through the cambium and youngest wood of Cytisus Labur- 

 num. 24-25. Ducts from Mahnnia 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.1 



