* 
40 VESTIGIAL AND RUDIMENTARY ORGANS IN PLANTS. 
petals, as in Canna, or into glandular nectaries, as in 
Parnassia, they are usually known as staminodes. In these 
extreme cases a transference of function has taken place, and 
although such instances show no degradation of structure, 
yet they illustrate how one organ may, in the course of time, 
have developed into another. More vestigial in their nature 
are the remnants of the stamens found in Zrodiwm. In this 
family one whorl of stamens has become vestigial, while in 
the allied Geraniacee both whorls are fully developed. 
Many instances may be found of one or more stamens of a 
whorl disappearing. This is especially the case in dorsi- 
ventral flowers. In such instances it appears to be the 
dorsiventral nature of the flower which has occasioned the 
reduction of the andreecium, The natural orders of the 
Orchidace, Labiate, and Scrophulariacee have typically 
dorsiventral flowers, and in most species belonging to these 
great orders the andrcecium is more or less incomplete. In 
the cases exemplified by the Scrophulariacez, the median 
posterior stamen is usually that which first undergoes 
reduction. In very few plants belonging to this large 
natural order is the staminal whorl complete, as in Verbascwm. 
In Pentstemon the filament of the stamen remains as a 
staminode, while in Mimulus the merest vestige at the base 
of the corolla is all that is left of this organ. In the large 
natural order of the Labiate, the stamen, which occupied the 
same position, has disappeared. The disappearance of this 
stamen in these flowers naturally leads to the conclusion that 
irregular or dorsiventral flowers have been derived from 
regular and symmetrical forms. The regular flower must 
therefore represent an earlier form of floral structure than 
the irregular or dorsiventral form. Many other plant-organs 
show reduction or degeneration, and it is sometimes difficult 
to explain why such changes have taken place, while in 
certain other cases the explanations are obvious. This 
branch of botanical study, however, possesses many attractions 
for those who are willing to pursue such a fascinating 
inquiry. 
