26 THE BOOK OF NATURE STUDY 



pairs of leaflets. These stand opposite to one another, and each 

 is borne on a short, translucent, swollen, stalk from which the 

 oval leaf-blade widens out. The leaflet is traversed by a midrib, 

 and its margin may be slightly toothed. The tip of the leaflet 

 may either be pointed or truncated, appearing as if cut off. The 

 stout leaf-stalk below the lowest pair of leaflets is of considerable 

 length. To either side of the base of the leaf-stalk where it springs 

 from the stem is a large leafy stipule. The stipules are much larger 

 than the leaflets, and provide a considerable part of the green 

 leafy surface of the plant. Each stipule is inserted by a wide 

 base, and, though the two do not join, extends for some distance 

 round the stem. The outline of the stipule is oval, the lower side 

 being more developed especially at the base, where also the margin 

 is toothed. 



On considering the construction of this leaf we can readily see 

 that it is derived from the compound pinnate leaf with a pair of 

 stipules at the base, so common in the family to which the Pea 

 belongs. The terminal leaflet and one or more of the uppermost 

 pairs of leaflets have been modified into tendrils. These are 

 sensitive to contact, and wind round any slender support so as to 

 grasp it firmly. They thus serve, as an examination of the relation 

 of the Pea plant to the supporting pea-stakes will show, to sustain 

 the whole plant and render unnecessary the development of a 

 stem strong enough to support the weight above. That the 

 tendrils are here modified leaflets is shown by the not infrequent 

 occurrence of intermediate structures or the presence of a leaflet 

 on one side and a tendril on the other. 



In the axil of each leaf is a bud, some of which may develop 

 further as lateral branches resembling the main shoot. The 

 buds in the axils of the upper leaves develop into inflorescences. 

 The inflorescence has a long smooth stalk, and ends in a pointed 

 tip. Towards the upper end it bears one, two, or sometimes 

 more flowers, which stand laterally, though the bracts below the 

 flowers are merely represented by a slight projecting rim. 



The flower itself has a short but distinct flower-stalk, and is 

 of the characteristic irregular form already studied in the Bird's- 

 foot Trefoil. It consists of calyx, corolla, stamens, and pistil. If 

 a flower is cut through the middle, the flower-stalk will be seen to 



