CHAP, iv.] REPRODUCTION OF PLANTS. 127 



abouts of nectar their food the corolla is a feature of 

 the reproductive portion peculiar to phanerogams for the 

 purpose indicated above ; the equivalent of the calyx as 

 a protective organ being present in some cryptogams, as 

 mosses. Following the calyx and corolla are the stamens 

 and pistil, the essential organs. At the present day 

 the flowers of numerous plants do not possess all the 

 parts mentioned above ; of the two essential whorls, some 

 flowers have stamens only, and others of the same 

 species pistils only, but the order of arrangement of the 

 parts present, and the vestiges of the missing whorls in 

 a more or less rudimentary condition suggests that the 

 earliest flowers were hermaphrodite, that is, having 

 stamens and pistil present, and such were in all proba- 

 bility self- fertilized. 



In Gymnosperms the flowers are unisexual, the stami- 

 nate and pistillate flowers being in some species present 

 on the same plant monoecious as in the Scotch fir 

 (Pinus sylvestris) , or the male and female plants are en 

 different plants dioecious as in the yew (Taxus baccata), 

 or as in the juniper (Juniperus communis) the male and 

 female flowers are sometimes on distinct plants, some- 

 times on the same plant, in fact, in cases where the sexes 

 are nominally separated at the present day it is not 

 unusual to meet with all stages of reversion to the old 

 bisexual or hermaphrodite type of flower, clearly indicating 

 the origin of the modern unisex'ual type as being due to 

 the suppression or non-development of one of the two 

 essential whorls for the purpose of preventing self- 

 fertilization. Many Angiosperms also have unisexual 

 flowers, monoecious as in the hazel, arum, etc., dioecious, 

 as the willows, poplars, and hop. The earliest idea in 



