CHAPTER IX. 
PHYSIOLOGY OF THE FLOWER. 
Tue 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 
(1.) 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. 118). Other animals have been 
called ‘‘unbidden guests.” Some, ¢.g., browsing animals, would 
devour the flowers altogether, if not deterred in some way; 
others, of which small wingless insects are the most notorious, 
would carry off pollen or nectar without conferring equivalent 
benefit. Protection against these attacks is secured in various 
ways, more or less complete, hut 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, &c., upon the 
leaves and stems. Bracts are very often prickly, as, for instance, 
those making up the involucre of a thistle. 
(6.) 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 
