ABNORMALITIES IN INFLORESCENCE OF SPIRAEA VANHOUTTEI 635 
- These seriations bring out clearly that there are minimum fre- 
quencies on four flowers per pedicel, and that the number of pedicels 
increases rapidly as the number of flowers becomes smaller, reaching a 
maximum on the single flowered (normal) pedicel, and that on the 
other hand it increases more gradually as the number of flowers 
becomes larger to a secondary maximum on 8-10 flowers per pedicel. 
Concluding Remarks 
This paper provides illustrations of the chief types of variation 
which occur in the inflorescence of Spiraea Vanhouttei, and records 
the results of statistical studies of the distribution of these abnormal- 
ities. 
The inflorescence of S. Vanhouttei is described by taxonomists as a 
simple raceme-like umbel. A number of the pedicels are^ however, 
often compound. The compounding may range from a simple 
synanthous condition to the production of a perfect, many-flowered, 
secondary umbel in the place of the solitary flower which normally 
terminates the pedicel. 
The distribution of abnormal pedicels among the inflorescences in 
plants in which abnormality is of frequent occurrence is not to be 
represented by a normal or Quetelet's curve but forms a one-sided 
or skew frequency distribution, in which the frequency of occurrence 
decreases as the number of abnormal pedicels per inflorescence becomes 
larger. This is the first law of variation in the abnormalities of the 
inflorescence. 
If the normal pedicels be included with the abnormal to form a 
single frequency distribution of number of flowers per pedicel in 
inflorescences in which some of the pedicels are abnormal, it will be 
seen that the two flowered pedicels form a transition frequency from 
classes of larger numbers of flowers to those with a single flower per 
inflorescence. 
On examining these bimodal frequency distributions the reader 
may be tempted to formulate some hypotheses concerning the co- 
existence of determiners of mutually exclusive characters or con- 
cerning the segregation of alternative, but variable, characters in 
the morphogenetic processes of the individual plants. S. Vanhouttei 
is known to be of garden origin and is supposedly a hybrid between 
S. cantoniensis and S. trilohata. The evidences are not, however, 
