CHAPTER IX. 



PHYSIOLOGY OF THE FLOWER. 



The flower, as a whole, is, of course, supported by the stem, and, 

 as in other cases (but here to a less extent), the various parts 

 are rendered firm by vascular bundles. Flowers need protection 

 (i.) from certain animals, (2.) from the weather. 



As regards animals, many insects, especially winged ones, and 

 more rarely birds, are "bidden guests." For them nectar is 

 excreted, and, in many cases, an otherwise unnecessary amount 

 of pollen developed. For these favours, as we shall see, uncon- 

 scious returns are made (p. 11S). Other animals have been 

 called "unbidden guests." Some, e.g., browsing animals, would 

 devour the flowers altogether, if not deterred in some way : 

 others, of which small wingless insects are the most important, 

 would carry off pollen or nectar without conferring equivalent 

 benefit. Protection against these attacks is secured in various 

 ways, more or less complete, but rarely entirely so. It is here 

 important to point out that one of the chief uses of the perianth 

 is to protect the essential organs, the pollen and the nectar. 



Protection from Animals. — (a.) Browsing animals, as also soft- 

 bodied insects, caterpillars, and snails, are kept off to a large 

 extent by the presence of thorns, spines, prickles, &&, upon the 

 leaves and stems. Bracts are very often prickly, as, for instance, 

 those making up the involucre of a thistle. 



(b.) Flowers always, or nearly always, contain (like some 

 foliage leaves) substances (as more particularly volatile oils) 

 which are distasteful to browsing animals and caterpillars. They 

 thus escape being eaten, and may even help to protect the foliage 

 leaves ; for when very small flowers are present in large numbers 

 among ordinary leaves, cattle will reject both. Dried flowers 

 mixed up with hay are, however, often eaten at once, as the 

 obnoxious substances are frequently volatile, and therefore dis- 

 appear in the process of drying. 



(c.) In countries where white ants are common, objects such 

 as tables can be protected by placing their legs in vessels of 

 water. Many plants keep off creeping insects in a similar way. 



