6 THE BROAD BEAN PLANT. 



15. The Shoot. The whole of the upper part of the bean- 

 plant, above the ground, may be called the shoot, as dis- 

 tinguished from the root, which grows in the soil. In 

 passing from the downward-growing axis or root to the 

 upward- growing axis or stem, what changes do you notice 

 in (a) shape of axis, (6) colour of axis, (c) nature of appen- 

 dages carried by the axis ? Note the four flat sides of the 

 stem, and its green colour, often tinged with red. We saw 

 that the root consists of a main cylindrical axis which is 

 covered at the tip by a root-cap and which bears as appen- 

 dages (a) root-hairs, (6) root-nodules, (c) rootlets which 

 repeat the form of the main axis and bear the same appen- 

 dages. What are the appendages of the shoot-axis (stem)? 



(a] Some of these consist of a stalk which is grooved on 

 its upper surface, carries a number of thin flat outgrowths 

 on either side, and (usually) ends in a slender prolongation. 

 (&) Other appendages of the stem consist of a four-sided 

 stalk which carries appendages like (a), and which there- 

 fore repeats the form of the main stem itself and may be 

 called a branch of the stem, just as a rootlet is a branch 

 of the root. In many plants, e.g. Wallflower, the first 

 kind of stem-appendage consists of an undivided thin flat 

 piece ; such an appendage is called a simple leaf. The 

 corresponding appendage of the Bean is also a leaf, but 

 here the leaf is compound, its thin flat portion being divided 

 into several pieces, the leaflets. 



16. Air-Spaces in Shoot. You have noticed a central cavity in 

 some of the cross-sections. How far does this cavity extend in the 

 stem, and is it continuous ? Find out by slitting up the whole stem 

 from top to bottom. Does it run out into the branches and the leaves ? 

 What does it contain in the uninjured living stem ? Nearly fill a 

 large basin with hot water (just boiled), and notice what happens when 

 you place in it (a) a piece of stem only, with the cut ends previously 

 well plugged with plasticine, (6) a whole plant. 



The results of these simple experiments show that the whole shoot 

 contains air-spaces and that these communicate with the atmosphere 

 by openings scattered over the surface. From the number of bubbles 

 seen to escape, the leaves evidently have far more air-openings than 

 the stem. Which side of a leaflet, upper or lower, seems to have 

 most openings ? These air-openings are called stomates. 



17. Hard and Soft Tissues of Stem. Cut slices across the 

 stem at several places, starting with the uppermost (youngest) parts 



