6oo 
PHANEROGAMS. 
influences their order of succession and their divergence fronni one another. But since, 
notwithstanding the extraordinary variation of the other relations of form, the true 
position of the floral leaves varies but little — though it may often be difficult to determine 
— the knowledge of this position is often of great importance in the determination of the 
affinities of the species, and hence for purposes of classification. This is especially 
the case if we at the same time take into account the abortion of individual members 
which is here of so common occurrence, the multiplication of the parts which take place 
under certain circumstances, and their branching and cohesion. 
In order to facilitate a description of these relationships, it is necessary to explain 
certain terms and methods of description. 
In the first place it is important to denote the position of all the parts of a flower 
with respect to the mother-axis of the floral shoot. For this purpose the side of the 
flower which faces the mother-axis is termed the posterior, that which is most remote 
from it the anterior side. If a plane be imagined to divide the flower longitudinally from 
front to back, and to include the primary axis of the flower as well as that of the 
mother-shoot, this is the median plane of the flower, dividing it into a right and a left 
half. Floral leaves, as well as ovules and placentae, which are bisected longitudinally 
by the median plane, are said to have a median position, either posterior or anterior. 
If another plane is now imagined at right angles to the first, and also including the axis 
of the flower, it may be termed the lateral plane; this plane divides the flower into a 
posterior and an anterior half, and parts which are longitudinally bisected by it are 
precisely lateral. The two planes which bisect the right angle between the median 
and the lateral planes may be called diagonal planes, and the parts which are bisected by 
them be said to have a diagonal position. Flowers usually have some of their floral 
organs placed exactly posteriorly or anteriorly, not so commonly exactly right and 
left or exactly diagonally; but usually other additional terms must be used, such as 
obliquely posterior or obliquely anterior. 
If next the position of the parts of the flower with respect to one another be ex- 
amined, their arrangement, as has already been mentioned, is either spiral or 'verticillate. 
Flowers with a spiral arrangement of their parts are comparatively rare, and appar- 
ently occur only in certain orders of Dicotyledons (Ranunculaceae, Nymphaeaceae, 
Magnoliaceae, and Calycanthaceae). Braun has termed such flowers acyclic, when the 
transition from one foliar series to another, as from calyx to corolla or from corolla 
to stamens, does not coincide with a definite number of turns of the spiral (as 
Nymphaeaceae and Helleborus odorus) ; hemicycUc when it does so coincide. This latter term 
may also be employed when some of the foliar structures are actually cyclic (verticillate), 
others spiral, as in Ranunculus, where the calyx and corolla form two alternating whorls, 
followed by the stamens and carpels arranged spirally. Parts which have a spiral 
arrangement sometimes occur in definite numbers, more often in larger indefinite 
numbers. 
When on the other hand the parts of the flowers are arranged in whorls, the number 
of the whorls, as well as that of the members of each whorl, is constant in the same 
species, and within larger or smaller circles of affinity ^. When the number of members 
^ [The number of whorls in a flower may vary very widely, from one {Carex) to fifteen or sixteen 
{Aquilegia). In some cases the calyx, corolla, androecium, and gynseceum each consists of a single 
whorl, so that the flower has four whorls. More commonly, however, one or other of these series 
consists of more than one whorl. This is most frequently the case in the androecium, so much so in 
fact that it is customary to regard the typical flower as containing two whorls of stamens : in an 
isomerous flower, if the stamens are in a single whorl it is said to be isostemotious, if in two whorls 
diplostemonoiis, and so on. The calyx often consists of more than one whorl (Menispermaceae, 
Berberidacese), and in most tetramerous flowers (Cruciferös, Onagraceae) it is composed of two 
decussating dimoerous whorls. More rarely the corolla consists of more than one whorl ; instances 
of this occur in the Fumariaceae, Berberidaceae, Papaveraceoe, Menispermacese. A gynaeceum of two, 
