THE GROWTH OF ROOTS AND STEMS. 165 



(c) To observe the continuity between the bundles of the stem 

 and those of the root, split a Bean seedling longitudinally in the 

 part where stem and root meet, and treat with caustic potash or aniline 

 chloride solution l ; the former makes the soft tissue transparent, the 

 latter stains the hard woody tissue yellow. 



196. The Vegetable Marrow (or the Cucumber) is a 

 suitable plant in which to study the tissues of the stem. 



* (a) Cut across the middle of several " internodes" in the older parts 

 of the shoot, and in each piece thus obtained notice that (1) the " node " 

 gives off a leaf, a special climbing organ (tendril), and usually either a 

 leafy branch or a flowering branch, or both ; (2) the internode is hollow, 

 so that the stem forms a tube, with (usually) five ridges, and furrows 

 alternating with these ; (3) the bundles (usually ten) are arranged in 

 two rings (a small outer bundle to each ridge, a larger inner one to 

 each furrow). 



(6) Scrape gently the outer surface of the stem, and remove part of 

 the epidermis or skin, which is thin and colourless and bears hairs, some 

 of them large and prickly. Notice the soft tissue which lies between 

 the bundles ; this is the ground tissue (parenchyma), and its cells can 

 easily be seen with a lens. After removing the epidermis, scrape away 

 the soft tissue which lies below it, and notice the hard tissue, which 

 forms a wavy tube around the stem, outside of the bundles. Slit a 

 piece of stem by two longitudinal cuts, and by scraping isolate a strip 

 of this hard tissue (sclerenchyma). Bend it, pull it by the two ends, 

 and try to split it ; notice that it is easily split longitudinally, but 

 is difficult to break by pulling at the ends. This hard tissue, then, is 

 fibrous, very strong, and it gives mechanical support to the stem ; it is 

 really a part of the ground-tissue, which has become fibrous and hard. 



(c) Now examine the bundles which are embedded in the soft 

 ground-tissue within the sheath or tube of hard tissue. Notice in 

 each bundle (1) a whitish hard portion, consisting chiefly of tubes of 

 various sizes, and occupying the centre of the bundle ; (2) two greenish 

 soft portions on the inner and outer sides of the hard portion. Place a 

 piece of the living shoot with its cut end dipping into red ink, and 

 notice that the ink rises in the middle portion of each bundle. This 

 portion is the wood, and the tubes it contains are the vessels, which 

 carry water upwards from the root. Split a long piece of stem so as 

 to get a strip containing a single bundle ; put one end into a glass of 

 water and blow through the other, noting the air which escapes in 

 bubbles after passing through the vessels. This shows that the vessels 

 are long, open tubes. 



1 Dissolve some aniline chloride (about l|d. per ounce) in a little 

 alcohol, add water to make a 10% solution, then a little hydrochloric 

 acid. A wooden match, or a splinter of wood, turns bright yellow 

 after being dipped into the solution, which gives a ready test for 

 woody substance (lignin). 



