IOWA ACADEMY OF SCIENCE 
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conclusions of his own as the Phytogeny of the group, together with the 
evidence on which the conclusions rest. 
1. Spiral character of the Aroids: It is the commonly accepted 
theory that the spiral arrangement is older than the cyclic. This seems 
reasonable, since the cycles of floral parts may be conceived of as a 
reduced spiral, and the position of the organs in such cases bears out 
this interpretation. The fact that the outer organs, may become cyclic 
while the inner remain spiral also fits in with the theory, and when in 
addition to this. one reflects that in the Dicotyledons spirality appears 
only in the Archiclamydeae, while the younger and more highly special- 
ized Sympetalae shows no sign of it, the weight of evidence seems quite 
conclusive. The theory is well expressed by Coulter & Chamberlain as 
follows : 
Among the most primitive flowers the floral axis tends to elongate, and the 
members appear in indefinite numbers along a low spiral. In more highly 
developed flowers the growth of the axis in length is checked at a very early 
period, so that the spiral along which the members successively appear be- 
comes lower and lower, until it has only a theoretical existence, passing into 
successive cycles, which eventually become limited in number. With the ap- 
pearance of definite cycles, the number of members appearing in each one be- 
comes limited, the limit in Monocotyledons being prevailingly three, and in 
Dicotyledons five or four. It is to be noted that the cyclic arrangement is 
not attained simultaneously by all parts of the flower. For example, in many 
species of Ranunculus the sepals and petals are cyclic, or approximately so, 
while the stamens and carpels are distinctly spiral. This tendency is so well 
marked that Engler has used it as a basis for dividing Monocotyledons into 
two great series, the “spiral series” comprising all those families that show 
the spiral tendency in any of the floral sets, and the “cyclic series” comprising 
all those whose flowers are completely cyclic, the former series including all 
the more primitive families. There is no reason why this same distinction 
cannot be applied also in a general way in the Archichlamydeae. This gradual 
transition of flowers from the spiral to the cyclic condition is one of the 
best marked tendencies in their evolution, and has the advantage of being 
represented by innumerable intermediate stages. All of those families which 
are now recognized as being of the highest rank have completely cyclic flowers, 
with members appearing in definite and low numbers, notably illustrated by 
the whole group Sympetalae. — (Morphology of Angiosperms, p. 11.) 
It should be borne in mind that these words refer in no way to the 
arrangement of the blossoms on the stalk, but simply and solely to the 
arrangement of the sepals, petals, stamens, and carpels, in the individual 
blossom. So far as the arrangement of floral parts is concerned, the 
course of evolution appears to have been in the direction of progressive 
reduction of the axis, resulting in a shorter and shorter spiral, and cul- 
minating in a completely cyclic condition. 
