8 THE BOOK OF NATURE STUDY 



stems spring from the old tuber, which by now has almost decayed, 

 only the corky layer which resists decomposition remaining. The 

 main stem continues up through the soil into the green foliage- 

 shoot. The lower portions covered by the soil and not exposed 

 to the light have a whitish colour, and bear only small scale- 

 leaves. In the axils of some of the scales thin cylindrical branches 

 arise which grow out horizontally around the base of the plant, 

 and in turn bear scale-leaves and branch. These branches swell 

 at the ends, and form the round or oval tubers. Many of the 

 tubers remain small, but a number, varying with the strength 

 of the plant and the particular kind, enlarge greatly. The roots 

 of the plant spring chiefly from the main stem. A number arise 

 from the base of this just where it emerged from the parent tuber, 

 but others spring from the nodes, so that the base of each under- 

 ground branch is accompanied by a group of roots. 



The shoot consists of a soft green stem bearing the foliage- 

 leaves singly at the nodes. The stem is winged, the thin ridges 

 or wings continuing down from either side of the insertion of 

 each leaf. A bud stands in each leaf-axil, and the shoot may be 

 more or less branched. The leaf is a compound one, its blade being 

 pinnately branched. The leaflets, which stand in pairs on the 

 continuation of the almost cylindrical leaf-stalk, are oval and 

 pointed. A noticeable peculiarity of the leaf is the occurrence 

 of small leaflets between the pairs of full-sized ones. 



The aerial shoots of the Potato end in inflorescences. The 

 inflorescence has a long bare stalk, at the summit of which is 

 a rather complicated branch system bearing the flowers. Only 

 minute bracts are present in relation to the flower-stalks. The 

 purple or white flowers open in succession, the terminal one being 

 the first to expand. Each flower is borne on a rather long stalk, 

 which has a distinct joint dividing a lower from an upper portion. 

 The latter, which belongs more intimately to the flower, may 

 have a purplish colour and falls off with the withered flower. The 

 flower-stalks, like the stem of the whole inflorescence, are hairy. 



Each flower consists of a calyx composed of five long pointed 

 sepals, which are free for the greater part of their length, but 

 united at the base. Within this comes the corolla composed of 

 five united petals, which alternate with the sepals. The corolla- 



