"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 tliree constantly recurring forms ; namely, 

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



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. Trartiei'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 ; the elements separated by maceration. 

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

 clieid. 23. Cross-section througli tlie cambium and youngest wood of Cytisus Labur- 

 num. 24-2~>. Ducts from MaliouiaAqnifolium. 24. After maceration. 25. Longitudinal 

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

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

 35. Spirally marlted duct from Vitis vinifera, after macerntion. 36. Libriform fibre 

 from Jatropha Manihot. (Sanio.) 



