AUTOGAMY BY A CO-OPERATION OF MOVEMENTS. 889 



meadows sometimes have no opportunity of becoming nutant. In them, as might 

 be expected, autogamy fails, and if the weather is bad, and no humble-bees are 

 about, cross-fertilization may also be prevented; therefore it is not unusual to find 

 many ovaries unproductive in level places of the kind. 



The Pasque-flowers, Anemone Pulsatilla and A. vernalis, may be taken as 

 representatives of the cases in which autogamy is achieved by means of an inflection 

 of the pedicels combined with an elongation of the sepals. The flowers of these 

 plants have very short stalks and face the sky when they first open. They remain 

 in that position for about forty-eight hours, opening in the daytime when it is fine, 

 and closing at night and when it rains. No drooping of the flowers is to be per- 

 ceived during the first two days, and indeed such a change would scarcely be possible, 

 considering the shortness of the stalks. The flowers are markedly protogynous. 

 The stamens are crowded together in large numbers, and their closed anthers, 

 grouped in the middle of the flower, resemble the grains of a head of maize. Above 

 the anthers rises a sheaf of styles bearing mature stigmas. Insects, especially hive- 

 and humble-bees, are attracted at this stage of floral development by the honey 

 which is secreted by small club-shaped nectaries interspersed amongst the sepals 

 and stamens. On entering a flower they rub against the sheaf of stigmas, even if 

 they have not actually used it as an alighting-place, and, in the event of their 

 bodies having been besmeared with the pollen of older flowers, a cross with some 

 plant which may be either of the same or of another species ensues. When two 

 days have elapsed, the aspect of affairs is altogether changed. The peduncle has 

 become considerably longer, and the flower nods slightly when darkness sets in; the 

 inner stamens are no longer stiff" but curve outwards, whilst those anthers which 

 are nearest to the styles have undergone dehiscence and offer their pollen for 

 dispersion. The sepals, which are concave towards the middle of the flower, have 

 elongated somewhat to protect the pollen. Insects now come in quest of pollen as 

 well as honey, and are certain to get dusted with a quantity of it which they may 

 then transport to other flowers. When a flower closes in the evening, pollen from 

 the anthers of the reflexed stamens is invariably affixed to the inner surface of the 

 superincumbent sepals. At this stage, too, pollen is liable to be shaken out of the 

 anthers of the longest stamens, and this falls, in the case of a nodding flower, on to 

 the central stigmas of the fascicle of styles. Two days later, again, the condition of 

 the flower is as follows: — The stalk is from ten to twenty times as long as it was, 

 and the flower is nutant in the daytime as well as by night. The stamens have all 

 relaxed from their rigidity; the filaments are curved outwards, and the anthers are 

 open. The sepals have more than doubled their original length, and the pollen 

 aflBxed to their inner surfaces has consequently been raised to the level of the 

 stigmas. In addition, the form of the three inner sepals has changed; the concave 

 inner face is now convex, and the external surface is concave. The result of these 

 changes is that the stigmas at the periphery of the fascicle now receive their share 

 from the elongated sepals, which are appressed to them and yield up to their 

 receptive tissue the pollen sticking to their inner surfaces. 



