REPRODUCTION. 



215 



_ 



FIG. 135. Spikelet of rye with 

 two flowers. 



three stamens and the pistil. 



is carried to the stigmas of other plants of the same species, and 

 they in return receive pollen from other plants. The transfer is 

 made by insects, and such flowers are 

 said to be entomophilous. The petals 

 of the corolla are either united or free 

 in the different groups of angiosperms. 

 They often have peculiar adaptations 

 of form to facilitate the fertilization 

 by insects. Different odors, sometimes 

 pleasant and sometimes very disagree 

 able, as well as various glandular secre- 

 tions (nectaries) serve a to attract insects. 

 Why the organ known as calyx, 



which may consist of either separate or 



J 

 united sepals, is absent in number 2 has 



already been explained. In Hyacinthns 

 there is no differentiation into calyx 



-, IT T.-, -. ,-, , . 



and corolla, while both are present in 

 Prunus (4. See Fig. 138). The calyx by its position and greater 

 firmness protects the younger and more delicate parts of the flower. 

 It would, of course, be functionless if other organs were adapted to 

 perform this protective function. There is besides Hyacinthus a large 

 series of monocotyledon ous flowers in which the calyx is normally 

 absent. Floral coverings which consist of equal or nearly equal leaf- 

 like organs without any distinction as to calyx and corolla are known 

 as i\\Q perianth. In its appearance it may resemble either the calyx 

 or corolla. It is remarkable that these ' ' apetalous ' ' monocotyle- 

 dons (orchids, aroids, onions) are equipped with larger or smaller 

 hypsophyllary leaves in the axils of which the young individual 

 flower (orchids) or the young inflorescence (aroids, onions) finds a 

 suitable protection. Further, it is noticeable that among many of 

 the apetalous flowers the rather firm perianth-leaves are green at 

 first and enclose the flower-bud; later they unfold and take on 

 bright colors. In the first stage they resemble the calyx in appear- 

 ance and function ; in the second stage they resemble more nearly 

 the corolla. In Fritillaria imperialis, a plant belonging to the 

 same group as 3, special organs occur at the base of the perianth- 

 leaves which secrete a saccharine liquid ; they are known as nec- 

 taries and are found in various flowers. Their function has already 



