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PHYLLOTAXIS OF SPECULARIA PERFOLIATA. 
F. M. Aprews. Indiana University. 
Leaf arrangement in plants has always-.been a point of interest a1.4d has 
been the subject of much study. Some plants have a very open or loose 
arrangement of their leaves as when they are separated by considerable 
distances on the stem as in some alternate or opposite leaves. The number 
or arrangement becomes greater and denser in other plants until their leaves 
form rosettes or culsters as in the common Houseleek. Or again as in the 
cones of the genus Pinus whose scale-like leaves often form conical-like 
cylinders of closely set divisions. Various theories were long ago advanced 
to explain the arrangement of leaces on the stem and especially by Cesalpino 
and Bonnet that the arrangement on the stem is in keeping with definite 
“ceometrical rules’. Also many others among them A. F. Schimper had 
formulated a theory on the subject. An excellent summary of many of the 
facts on this subject has been collected by Sachs. But the effort of the 
plant is to arrange the leaves on its stem in such a manner that they will 
have the best exposure to the light. Also the question of structural phy- 
sical factors in the plant itself enter into the placing of leaves on the stem. 
The arrangement which a given species shows is followed by all individuals 
of that species although, as will be seen later, this may be departed from 
to a certain extent. This difference I found rather markedly shown in 
the spiral arrangement of the leaves of Specularia perfoliata. Gray* de- 
scribes Specularia perfoliata as follows: “Somewhat hairy, 1-9, dm, high, 
leaves roundish or ovate, clasping by the heart-shaped base, toothed, flow- 
ers sessile, solitary or 2-3 together in the axils, only the upper or later 
ones having a conspicuous and expanding corolla, capsule ellipsoid, short, 
straight, opening rather below the middle; seeds lenticular”. 
Nothing is said by Gray, Britton. or Wood about the rather marked and 
regular arrangement of the leaves on the stem of this plant in spirals. This 
arrangement together with the form of the leaves is a striking characteristic 
of Specularia perfoliata, and reminds one but to a much less degree of the 
unusually “spirally twisted raceme” of flowers of Spiranthes gracilis. 
When making a trip into Brown County, Indiana, during the summer of 
1920, I noticed by the roadside about one mile from Belmont, near the studio 
of the artist, Dr. T. C. Steele, a large number of specimens of Specularia 
perfoliata. Most of these plants were of normal size and appearance. 
Their leaves were arranged on the stem in the usual way and as to number 
showed four to a single turn of the stalk which is the ordinary number. 
Also ordinarily three circuits of the stem must be made before a leaf will 
be found that will stand on the stem directly above the first leaf with which 
the count was begun. In other words the twelfth leaf, counting the one at 
the starting point, will stand directly over this first one where the spiral 
Was originally started toward the base of the stem. In this arrange- 
1Sachs, J. History of Botany 1875 P. 163. 
*Sacks J., History of Botany 1875 P. 162. 
*Sachs, J. History of oBtany 1875, Chapter 4, PP. 155-181. 
‘Gray, A. New Manual of Botany, 7th edition. 
