PHANEBOQAMIA. 235 



distance. In sunflowers, in addition, the marginal flowers 

 in the cluster develop an especially showy perianth, sur- 

 rounding the whole with conspicuous rays. 



600. Many showy flowers have no nectar (honey) glands, 

 but in general some part of the flower secretes a sweet, 

 sugary fluid which is attractive to insects and some birds. 

 The nectar is always situated in the back part of the flower, 

 so that in securing it the insect is obliged to come near to 

 the pollen-sacs or stigma. 



501. In this connection the various irregularities of size 

 and form in the parts of the perianth, as well as of stamens 

 and pistils, have a meaning. Thus the perianth-leaves may 

 grow together into a tube, in which case the nectar is at 

 its bottom; or they may be of different sizes, as in orchids, 

 beans, peas, etc., where they are so placed as to admit of 

 access to the nectar from one direction only. In some 

 tubular flowers there are two forms in the same species, 

 those of some plants having long stamens and short styles, 

 while in others the structure is exactly the reverse. Insects 

 in getting honey from these will pollinate the long-styled 

 flowers with pollen from the long stamens of other flowers, 

 and vice versa. There is also very often a greater or less 

 difference in the time of maturity of the stamens and pis- 

 tils. In some the pollen is set free before the stigma ie 

 ready for pollination; in others it is the reverse. .This (and 

 the preceding) arrangement prevents pollination of a pistil 

 by pollen from the stamens of the same flower; i.e., close 

 fertilization is prevented. 



502. Self-pollinated (autogamous) flowers are much less 

 numerous than those which are wind- or insect-pollinated, 

 and it is doubtful whether there are any species of plants 

 all of T^hose flo'vyers exhibit constant self-pollination (au- 



