HISTOLOGY OF ANGIOSPERM STEM, ROOT, ETC. Ill 



examine the roots, and note the presence, absence, and rela- 

 tive abundance of root-hairs in the four cases. In the roots 

 grown in soil, note that the root-hairs are irregular in form 

 and are often branched at the tips, to which soil- particles 

 may cling even after the roots have been well rinsed in 

 water. 



128. Xylem Vessels in the Root. Cut the slender 

 root of a seedling e.g. Mustard or Cress into pieces about 

 1 cm. long. Mount in water all the pieces, or at any rate 

 some taken from different regions starting at the youngest 

 (that nearest the root-cap), and crush them under the cover- 

 glass, and examine. Treat with aniline sulphate and note 

 especially the xylem vessels < some are narrow spiral (pro- 

 toxylem) vessels, others wider and pitted. 



Prove, by crushing the root in this way, or by clearing it 

 with potash, that only the spiral vessels are present in the 

 younger parts of the root, also that these first-formed spiral 

 vessels lie near the outside of the vascular cylinder, while 

 the later-formed pitted vessels are developed internally to 

 them towards the centre of the cylinder. 



129, General Anatomy of Bean Hoot. Examine well- 

 grown roots (about 15 cm. long) of seedling Beans ; or dig 

 up Broad or Runner Bean plants growing in garden soil, 

 and rinse the roots in water. 



(a) Note that each rootlet emerges from a slit in the 

 surface of the main root. Cut across the main root so as 

 to cut one or more of the rootlets longitudinally, clear with 

 potash if necessary, and note that each rootlet arises from 

 the central cylinder. 



(6) Scrape the soft outer tissue (cortex) from an old part 

 of the root, and note the hardness of the cylinder ; mount 

 a piece of the latter in aniline sulphate, tease it out or crush 

 it on the slide, and look for the spiral and pitted vessels. 

 By scraping the cortex from the place where a rootlet is 

 given off, and treating with aniline sulphate, prove that 

 there is continuity between the vascular cylinder of the 

 rootlet and that of the main root. 



