566 Insects and Flowers 



same flower) different in length so that the pollen would be unlikely to fall 

 on the stigmas, or (d) the having the stamens and pistils so situate with 

 regard to each other that it is difficult or very unusual for the pollen to reach 

 a stigma. All these devices are familiar to every student of botany, and 

 to gardeners, florists, and flower-lovers generally, and examples of them all 

 can readily be found among our common garden and field plants. Any 

 simple manual of botany will put one in the way of hunting them out for 

 one's self. 



To recur now to the first of the two principal lines of specialization 

 referred to as those which have arisen in connection with the advantage 

 of cross-pollination, namely, the modification of the floral structures, we 

 shall find these modifications to consist of (a) the secretion of nectar to 

 attract the insects, (b) the development of odor, color, pattern, and shape 

 to guide them to the flower and when there to the nectar and pollen in such 

 a way as to insure their brushing against both, or either, pollen and stigma, 

 (c) the modification of shape so as to prevent the stealing of nectar and 

 pollen by non-helpful insects, and (d) the blossoming at those times in 

 the year (seasonal flowering) when the particularly helpful insects are most 

 numerous, and the opening of the flowers at such times, in daylight, twilight, 

 or at night, as specifically accords with the food-seeking flights of these 

 insects. The manifold variety of these modifications will be indicated and 

 illustrated by accounts of a few specific cases exemplifying certain more 

 or less distinct kinds of modification and reciprocal relation with insects, 

 but a few general statements may first be made. 



The pollen collected for food by the bees and a few other insects is, of 

 course, a normal product of the flower, and it is only necessary that there 

 be enough of it to supply the insects and yet suffice for the plant's own uses, 

 i.e., in fertilization. As the oldest, the most primitive, means developed 

 among plants to effect cross-pollination, a means still used by all the conifers, 

 the grasses, and many other plants mostly characterized by the total absence 

 of colored floral envelopes (petals and sepals), is the production of vast quan- 

 tities of light, non-adherent, pollen grains to be distributed by the wind, 

 the more specialized entomophilous flowers (those depending on insects 

 to carry their pollen) probably started with enough and mora of pollen to 

 supply their own needs as well as the demands of their visitors. 



The nectar, however, is a special product, developed in direct connection 

 with the insect pollinating specialization. It is a "more or less watery solu- 

 tion of sugar and of certain salts and aromatic substances secreted by a 

 special tissue known as the nectary and expelled at the surface through the 

 epidermis by breaking down of the tissues, or through a special opening 

 of the nature of a stoma. The nectar either remains clinging to the surface 

 of the nectary or it gathers in large drops and falls into a nectar receptacle 



