THE BROAD BEAN PLANT. 9 



23. The Leaf-Stalk (Petiole). Note the groove on the upper 

 surface, making the leaf-stalk gutter-shaped. What does this com- 

 parison with a gutter suggest as to the use of the groove in wet 

 weather ? Test the matter by a simple experiment with a watering- 

 pot, or watch a plant during a shower of rain. 



What about the narrow prolonged tip at the end of the leaf-stalk ? 

 The nearest relatives of the Broad Bean are the Vetches and Peas, 

 which differ from our type in being weak-stemmed climbing plants, 

 the upper leaflets of their leaves being modified into slender organs 

 (tendrils) which coil around supports. Get any of these (e.g. Sweet 

 Peas) and compare their leaves with that of the Broad Bean. What 

 light does the comparison throw on the nature of this part of the 

 Broad Bean leaf ? A special organ used for climbing is called a tendril. 

 Make out with the lens the structure of the leaf-stalk. How are the 

 bundles arranged ? Is there a central air-channel, and is it continuous 

 with the air-channel of the stem, or the branch, that bears the 

 leaf? 



24. Branches and Buds. You will have noticed that 

 each branch of the stem arises just above the base of a 

 leaf, and that as a rule they become shorter towards the 

 upper end of the stem. Pull off the young leaves at the 

 end of the stem or of a branch, to see the small young 

 branches (buds), one above the base of each leaf. These 

 buds are called axillary, the space between the leaf-base 

 and the part of the stem above it being called the axil 

 of the leaf. At the very end of the main stem and of 

 each branch there is a terminal bud. A bud is simply a 

 young shoot, consisting of a short axis (stem) bearing 

 young leaves which are closely crowded together and overlap 

 the growing apex of the axis. Later on, the stem part of 

 the bud grows in length and the leaves become spaced out 

 on it, as well as growing larger. 



The points on the stem where leaves come off are called 

 nodes, the parts between the nodes being called internodes ; 

 but these names, though useful in describing plants, are 

 often associated with a false conception of the shoot as 

 being made up of " joints," each consisting of an internode 

 and a node bearing one or more leaves. The node is 

 merely a place where a leaf stands on the stem, and 

 where the bundles of the stem divide and join with those 

 of the leaf and also with each other, causing a swell- 

 ing. 



