536 SECONDARr CHANGES. 



same regions in all Umbelliferae, and in the Araliaceae ; where the bast is strongly 

 developed they form, as seen in transverse section, interrupted radial and concentric 

 series, differing in arrangement according to the species '. 



In the secondary bast of the stem and branches of Pittosporum Tobira, the 

 passages appear relatively late ; Van Tieghem found four concentric rows in a 

 branch lo™™ thick. They were not found in the secondary bast of the root of 

 this plant. 



Among the Compositae which contain passages, some also have them in the 

 secondary bast, e. g. Helianthus and Centaurea atropurpurea ; in Inula Helenium 

 the bast of the root contains wide passages, which are closed blindly, so far as is 

 known, at both ends, and coated by a delicate epithelium : they resemble those in 

 the secondary wood. Other Compositae have no passages in the region mentioned, 

 but, on the other hand, have sca'ttered sacs, filled with secretions, in the parenchyma 

 of the rays, e. g. Echinops and Tagetes patula (comp. p. 203). 



The Coniferse, which have such great numbers of protogenetic resin-passages 

 in their other tissues, do not form them in the secondary bast, except in a few 

 cases. The exceptions include, firstly, the blind ends of the horizontal passages in the 

 medullary rays of the Abietinese mentioned on p. 490, which extend into the zone of 

 bast. According to Van Tieghem, longitudinal passages occur In the secondary bast 

 of Araucaria Cookii and brasiliensis, and of Widdringtonia cupressoides, which were 

 mentioned on p. 443. The spaces filled with resin which occur in other Coniferae 

 are subsequent, hysterogenetic products of disorganisation, which will be discussed 

 in Sect. 173. 



Secretory sacs, other than those containing crystals, appear in the soft bast in the 

 plants mentioned in Sects. 33-35, and are sometimes scattered without any perceptible 

 regularity, while they sometimes have a definite arrangement, also stated in the 

 paragraphs mentioned. 



Sect. 165. The sckrenchymatms fibres of the bast, bast-fibres, or according to 

 the older terminology ' bast-cells ' in the strictest sense, have the form and structure 

 generally described in Chap. II. With reference to the latter, it may further be 

 mentioned that the lamella which forms their boundary, whether towards elements of 

 the soft-bast, or towards one another, is in these cases especially often an unlignified 

 membrane of cellulose, which surrounds the more or less lignified, thick membrane of 

 the fibre as a distinct sheath ^. Comp. Figs. 211, 212. 



The bast-fibres are entirely absent in the bast of many plants; both in its 

 secondary portion, and at the outer boundary of the primary phloem. This is the 

 case in the stems afld branches of Ribes, Viburnum Lantana', Pittosporum Tobira, 

 undulatifolium, Citriobatus multiflorus, Porlieria, Centradenia grandifolia, and Ber- 

 beris vulgaris, and in the roots of many herbaceous Dicotyledons. Thus they do 

 not universally form an essential constituent of the bast. In the cases where they 

 are present, which certainly form the majority, they occur — 



' Compare the figures of roots of Umbellifers in Wigand, Pharmacognosie. and Berg, Atlas, 

 Taf. 8, 9, 14, 22. 



* See Graf z. Solms-Lambach, Bot, Zeitg. 1871, p. 516, &c. 

 ^ Hanstein, Banmrinde, p. 17. 



