6 INTRODUCTION 



intolerable ; but it is always agreeable to the insects for which the nectar is destined. 

 The corolla is, except in a very few species, coloured, i. e. other than green, so that 

 it is conspicuous against the green colour of the plants. Sometimes the calyx also 

 is coloured, and when the corolla is developed, the calyx may be different from it, or 

 if it makes one whole with this, it is similarly coloured on the inner side. But if the 

 corolla is absent, then the calyx takes its place. ... If now an insect, attracted by the 

 beauty of the corolla, or by an agreeable odour, has gone to a flower, it will either 

 forthwith perceive the nectar, or, if this is in a concealed place, will not perceive it. 

 In the latter case Nature comes to the rescue with the nectar guide. This consists 

 of one or several spots, lines, dots, or markings of another colour than that of the 

 corolla as a whole, and consequently conspicuous against its lighter or darker 

 tint. It is always placed just where the insects inust creep in if they are to 

 reach the nectar.' 



'In connection with the nectar guide I must refer to the difference in nectar 

 flowers with regard to the time of day at which they open. As there are insects 

 that only move about in the daytime, so there are day flowers and night flowers. 

 The day flowers burst forth into bloom in the morning. Many of them close in 

 the evening, or incline downwards, while they stand erect by day. The day flowers 

 are adorned with nectar marks, though not in all cases. The night flowers 

 blossom in the evening. In the daytime most of them are closed or limp and 

 inconspicuous, from which it is clear that they are not destined for day insects. 

 The night flowers have a large and bright-coloured corolla, so that they are 

 conspicuous to the eyes of insects in the darkness of the night. If their corolla 

 is inconspicuous, the defect is made good by a powerful odour. No nectar 

 guides occur in them ; for if the white corolla of a night flower had a nectar 

 guide of another, but still light tint, this would not be conspicuous against the 

 colour of the corolla in the darkness of the night, and so would be useless ; 

 while if it had a dark-coloured nectar guide, this would be inconspicuous, and 

 would therefore be as useless as the other.' 



5. Pollination of nectar flowers by insects: Dichogamy. 'All these 

 arrangements are in the first place and immediately for the benefit of insects, but 

 through these also for the flowers themselves; and their final purpose is that the 

 flowers may be pollinated by insects. That insects play their part in the pollination 

 of flowers has already been remarked by others. So far as I know, Kolreuter 

 has gone furthest in this direction, as he discovered and clearly demonstrated 

 the fact in Iris, for instance, and a few other genera. No one, however, has yet 

 shown that the whole structure of nectar flowers points to this purpose, and can 

 be fully explained with reference to it, for no one has recognized what I call the 

 nectar cover and the nectar guide to be what they are, though every one has seen 

 them. . . . There is undeniable evidence of the pollination of flowers by insects in 

 the arrangement discovered by me in very many hermaphrodite flowers, which 

 secures that no individual may be fertilized by its own pollen, but only by pollen 

 from another individual. . . . This arrangement I call the development of sexual pans 

 (anther and stigma) at different times, or shortly, dichogamy. It consists in this ; 

 After the flower has opened, the filaments have or assume, either all together or 

 one after the other, a definite position, in which their anthers open, and their pollen 



