32 PB ACTIO AL GUIDE TO GABDEN PLANTS 



Spines or Thorns are also modified branches or leaves ; but the 

 prickles of the Eose and Blackberry are merely excrescences or cellular 

 outgrowths of the stem. 



Underground Stems. — Perhaps the best known form of an under- 

 ground stem is that of the Flag Iris (p. 917) and Solomon's Seal (p. 811). 

 They look like real roots but the leaf -like scales and buds show them to 

 be stems by nature. Many plants have underground and more or less 

 creeping stems, as in Lily of the Valley (p. 813), Mint (p. 744), and Couch- 

 grass, the latter on this account spreading rapidly and becoming a 

 nuisance, especially when chopped by hoeing &c. 



Underground stems are often thickened and serve as storehouses 

 for food during the winter in many plants with herbaceous stems. 

 They take many shapes, among which may be mentioned : 



The Tuber, as in the Potato (p. 1133), the Jerusalem Artichoke, the 

 ' eyes ' of which are leaf -buds from which stems arise (p. 1140); the Corm 

 or Solid Bulb, as in the Cyclamen (p. 626), Crocus (p. 936), and Gladio- 

 lus (p. 947) ; the Bulb, as in the Madonna Lily (p. 846), the Tulip 

 (p. 860), Hyacinth (p. 833), Onion (p. 1148) &c. 



In some plants the stems are so modified in form and structure that 

 they perform the functions of the foliage. The stems of many cacta- 

 ceous plants are of this nature, and also the branches of the Common 

 Butcher's Broom (see p. 810) which resemble leaves in appearance. 



THE LEAVES 



From definite points (called nodes or joints) of the stem and branches 

 leaves are developed and arranged more or less horizontally, vertically, 

 or drooping so as to obtain a greater or less amount of sunshine, and 

 to throw water towards or away from the main axis of the plant, accord- 

 ing to the nature of the species. 



It will be noticed for example that the leaves of Ehubarb (p. 770), 

 Arum Lily (p. 955) and other plants have the tips of the leaves uppermost. 

 They are more or less channelled down the centre, and water is by this 

 means transferred towards the centre of the plant, and down the stem 

 to the roots. In such plants it will generally be found that the roots 

 do not spread over large areas but are confined in a small space 

 beneath the centre of the plant. Many other plants on the contrary, 

 like most of our trees and shrubs and flowering plants, have the leaf- 

 tips pointed outwards and downwards so as to throw the water chiefly 

 around the circumference of the plant and away from the centre. In 

 plants with these peculiarities the roots spread out and away from the 



