VESTIGIAL AND RUDIMENTARY ORGANS IN PLANTS. 39 
many instances of vestigial and metamorphosed structures. Of 
a simple structure, and rudimentary as regards their perianth, 
are the flowers of the Amentacee. But the abundance of seed 
produced yearly by the members of this order of plants clearly 
proves that the essential organs of their flowers are actively 
functional. Their rudimentary character consists only in 
the absence or simple form of the perianth. This same 
character prevails among those plants whose flowers are 
fertilised by the agency of the wind. In the Amentacez 
and in the Conifere this simplicity of floral structure is 
a primitive feature, and the method of securing pollination 
by the wind is perfectly compatible with the absence of a 
brightly coloured perianth. It is a noteworthy fact that the 
flowers of the catkin-bearing trees are unisexual, and when 
it is considered that such orders as the Composite and 
Orchidacez, which have reached the highest state of develop- 
ment as regards their floral organs, are hermaphrodite, the 
inference is obvious that the ancestral forms of plants with 
unisexual flowers were probably very distinct from those 
types from which the trees with hermaphrodite flowers have 
sprung. Where wind-pollination is not a primary but a 
secondary feature, as is probably the case in grasses, vestigial 
organs, as might be expected, are to be found. The lodicules 
which force open the palez and glumes, when the pollen is 
ripe, are generally supposed to represent vestigial portions of 
the perianth. 
In some of the higher phanerogams, unisexuality has been 
brought about by the degeneration of one set of essential 
organs. In Lychnis diwrna some flowers are staminate, 
others pistillate. This arrangement of sporophylls has been 
caused by the partial or complete abortion of one set of 
organs whose vestiges are usually found in those flowers in 
which they have not been developed. In many of the more 
highly organised flowering plants, similar instances of the 
complete disappearance of the andreecium or gynecium are 
found, as in the sea-buckthorn (Hippophw rhamnoides), differ- 
ent species of Cucumber (Cucurbitacez), and Sedum Rhodiola 
(Crassulacee). The unisexual condition has doubtless been 
gradually produced in these plants with the aim of securing 
cross-fertilisation, When stamens are transformed into 
