Flowers. 175 



"While in the summer of 1787 I was studying some 

 species of Iris I soon found . . . that the nectar is fully 

 protected from the rain, and that there are specially 

 colored places which lead the insects to the nectar. But I 

 found still more, namely, that the flowers cannot possibly 

 be fertilized in any other way than by means of insects, 

 and in fact by insects of considerable size. . . . My in- 

 vestigations ever more and more convinced me that many, 

 indeed perhaps all, flowers which have nectar are fertilized 

 by the insects which obtain food from this nectar." 



Figure 90 is a reduced facsimile of the title-page of 

 Sprengel's book; the various flowers of the border -give 

 some idea of the variety of forms worked out by him. 



126. Devices for Cross Fertilization. The ability of 

 plants to adapt their members, by modifications of form and 

 structure, to various conditions and ends, is perhaps best 

 shown in the construction and behavior of their flowers. 

 The end which most flowers seek to attain, as long since 

 pointed out by Sprengel, is cross fertilization, and the 

 agents to which they have to adapt themselves are wind, 

 insects and other animals, and water. In order that cross 

 fertilization may be achieved it is of paramount importance 

 that self fertilization should be prevented, and we accord 

 ingly find special devices having this end in view. 



The chief of these devices are as follows : (i) Only one 

 sex is represented in each flower, but both sexes occur on 

 the same plant. The flowers which contains the stamens 

 are called staminate, while those which contain the pistils 

 are called pistillate ; the flowers in this case are called 

 monoecious (see Glossary for derivation of terms). (2) The 

 pistillate flowers only are borne on one plant, while the 

 staminate flowers are borne on another plant ; such flowers 

 are called di&cious. (3) The flowers contain both sexes, 



