THE BROAD BEAN PLANT. 7 



and working downwards. Arrange the slices in order on your glass 

 plate, cover with a little water, and examine with the lens. Note that 

 the young parts are solid and soft, while the older parts are hollow and 

 hard. Note the hard tissue lying within the soft green outer tissue. 

 In young parts the hard tissue consists of separate strings (bundles) 

 forming a ring of whitish points in cross-section ; note the extra 

 bundles lying outside of the ring, occupying two of the four projecting 

 corners (there is a small bundle in each of the corners alternating with 

 these two, but they are harder to see). In older parts the bundles are 

 joined in a continuous hollow cylinder or tube (a complete ring in cross- 

 section), but the extra bundles lie outside of this in the same positions 

 as in the young parts. 



Now run the water off and place on the sections a little aniline 

 chloride, noting the result. Cut the stem longitudinally into strips 

 and note the bundles, which will be easier to follow if the strips are 

 placed in potash solution (made by dissolving a stick of caustic potash 

 in water) for a short time. Scrape the soft outer tissue from a piece of 

 stem and notice the hardness of the bundles, especially in the older 

 parts. 



18. The Leaf. Each leaf consists of an axis (leaf-stalk) 

 which bears right and left a number of thin flat outgrowths. 

 The two lowest of these lie on each side at the base of the 

 leaf -stalk, close to the stem ; they are called stipules to 

 distinguish them from the leaflets carried higher up on the 

 stalk. The leaflets are rather variable in number, but we 

 usually find a pair close together, right and left, near the 

 top of the stalk, and from two to four spaced out on the 

 stalk below these. Note the difference in shape between the 

 leaflets (oval) and the stipules (triangular, like one lateral 

 half of a spear-head) ; what other differences do they show ? 

 Notice the slender outgrowth into which the leaf -stalk is 

 (usually) prolonged above the leaflets (Fig. 1). 



Do any of the leaves in your plants bear a leaflet in place 

 of this outgrowth, and do you find any leaves ending in 

 structures intermediate between these two extremes ? Note 

 that the leaf -stalk comes off at one of the ridges of the 

 stem, the stipules being against its two adjacent flat sides. 



19. Arrangement of Leaves. Follow the ridges along the stem, 

 and find out in how many rows the leaves are arranged. Do leaves 

 come off at all four ridges ? Do the ridge* run straight up and 

 down the stem, or is there any twisting ? Compare the leaf -arrange- 

 ment in the Broad Bean with that observed in other plants which have 

 square stems e.g. White or Red Dead-nettle, Mint, Figwort, Coleus 

 and note any differences. 



