CHAPTER I. GENERAL PHYSIOLOGY. 691 



(2). CatapJiyllary or Scaly Leaves (p. 58) serve to protect, 

 growing-points and young leaves of buds, and in this they are 

 assisted by the secreting-hairs (colleters, p. 144) which they 

 frequently bear : they sometimes serve as depositories of reserve 

 plastic materials (e.g. scales of Onion-bulb). 



(3). Floral Leaves. 



a. Hypsophyllary Leaves. The leaves included under this 

 head are the bracts (and bracteoles) and the perianth-leaves 

 (p. 59). 



When green, the bracts perform the ordinary functions of 

 foliage-leaves : but when they are collected around a flower 

 (epicalyx) or an inflorescence (e.g. involucre of Composite, 

 Euphorbia, etc.) they serve to protect the floral organs during 

 their development. When highly-coloured (e.g. in Araceae, 

 Euphorbiaceae, Nyctaginaceae), they serve to attract insects to 

 visit the otherwise inconspicuous flowers. 



The sepals, like the bracts, are commonly green, and then they 

 perform the ordinary functions of foliage-leaves, and also serve 

 to protect the other floral organs : when petaloid (e.g. many 

 Ranunculaceae and Liliales), they attract insects for the purpose of 

 cross-pollination. 



The petals are brightly-coloured in most flowers, and it is their 

 special function to attract insects. Not uncommonly they are 

 specially modified as nectaries (e.g. Helleborus), and thus further 

 contribute to ensure the visits of insects. 



The perianth-leaves (and sometimes also the bracts), are often 

 capable of performing movements leading to the opening and 

 closing of the flower or inflorescence : thus the flowers of the 

 Crocus, Tulip, and Poppy, and the inflorescence of the Daisy, open 

 under the influence of rising temperature and increasing intensity 

 of light, closing under the contrary conditions : the closing is a 

 protection of the essential floral organs against cold and wet ; it 

 is essentially similar to the nyctitropic movements of foliage- 

 leaves (see p. 689). 



b. Sporophyllary Leaves. As already stated (p. 77) the sporo- 

 phylls are the essential organs of the flower, when they are 

 aggregated on a special shoot, and have, in any case, the function 

 of asexually producing the spores. They are more or less generally 

 modified in form and structure in connexion with this function ; 

 and in the many different forms of flowers these leaves present 

 remarkable special adaptations which mainly refer to the process 



