HISTORICAL DEVELOPMENT OF FLOWER POLLINATION .5 



inferred from the part to the whole. If, thought I, the corolla is coloured at 

 one particular part specially for insects, then the whole colouring is for the benefit 

 of insects; and if the particular colour of one part of a flower serves to enable 

 an insect which has setded on the flower easily to find the right way to the 

 nectar, then the general colour of the corolla is serviceable in rendering the 

 flowers provided with it conspicuous even from afar to the eyes of insects that 

 hover around in the air, in search of food.' 



Even from these introductory words Sprengel's view of nature and his method, 

 as well as his keen power of observation, and the clearness and simplicity of his 

 mode of giving evidence may be recognized. 



Connected with the above discoveries is the invesdgation in the summer of 

 1789 of a few species of Iris, from which Sprengel concludes that fertilization 

 can only be eflfected with the help of insects. In the spring of the following 

 year he remarked ' that Orchis laiifolia and Orchis Morio have altogether the 

 structure of nectar flowers, but do not contain any nectar.' Nevertheless 'these 

 flowers are pollinated by certain flies which, deceived by their appearance, suppose 

 that there is nectar in the spur, and accordingly creep in; but when they do this, 

 they draw forth the pollen masses from their sacs, and carry them to the sticky 

 stigmas ^ Flowers of this sort which have quite the appearance of nectar flowers, 

 but do not contain nectar, I propose to call false nectar flowers.' 



In the summer of the same year Sprengel discovered that in Epilobium afigusti- 

 folium and in Nigella arvensis the stamens and carpels of one and the same flower 

 do not develop simultaneously, a phenomenon he described as dichogamy; and 

 when, in the spring of 1791, he found the 'female-male' (protogynous) dichogamy 

 of Euphorbia Cyparissias, he was able to set forth his theory of flowers : ' In all 

 those flowers which actually produce nectar, the following parts have to be 

 distinguished ' : 



1. The Nectary. 'This is the part of a nectar flower which prepares and 

 secretes the nectar.' . 



2. The Nectar Reservoir. ' This is the part of a nectar flower that receives 

 and contains the nectar that is secreted by the nectary.' 



3. Parts protecting the nectar from rain : the Nectar Cover. 'Nectar 

 flowers are so constructed that insects can readily get to the nectar, but drops of 

 rain, which fall on or into the flowers, always remain at some distance from the 

 nectar, and so cannot mix with or destroy it ^.' 



4. Parts that enable insects readily to find the nectar: Corolla, 

 Odour, Nectar Guides. Nature ' has taken care that insects may recognize flowers 

 even from afar, either by sight or by smell, or by both senses together. All nectar 

 flowers are adorned with a corolla, and very many give forth an odour, which, 

 as a rule, is pleasant to mankind, though frequently it is unpleasant, and occasionally 



^ Sprengel here overlooks the fact that the pollen masses are brought by the visiting insects, 

 not to the stigma of the same flower, but to that of another (cf. my edition of Sprengel, 

 I, p. 181). 



* The ' nectar cover ' of Sprengel protects the nectar in many cases, not so much from ram as 



from nectar-lhieves. 



