ABNORMALITIES IN INFLORESCENCE OF SPIRAEA VANHOUTTEI 625 
as a hybrid between Spiraea cantoniensis and S. trilohata, without 
giving any details or actual proof of its hybrid origin. 
Schneider^ follows Zabel in regarding the form as a hybrid between 
S. cantoniensis and S. trilohata. So far as I can make out there is no 
really valid ground for this conclusion. 
The early writers on S. vanhouttei noted abnormalities of the 
inflorescence. Briot^ describes some in the original material. Zabel^ 
has even described a new form, which he calls S. Vanhouttei var. 
phyllothyrsa, in part distinguished by abnormalities of the'inflorescence. 
Those who desire to compare the anomalies described in this 
paper with those hitherto recorded may consult these papers. My 
purpose has not been to describe in detail all the types of aberration 
which may occur, but rather to throw them into categories usable for 
statistical analysis. 
2. Descriptive Morphology of Inflorescence 
The normal inflorescence of S. Vanhouttei is a many-flowered umbel- 
like raceme. In general, the pedicels originate fairly close together, 
but occasionally the lowermost flowers are considerably scattered. 
Normally each ray, as I shall sometimes call the pedicels, is simple, 
terminated by a single flower, but occasionally more or less com- 
pounded. The normal inflorescence, composed exclusively of simple 
rays, is too familiar to require illustration. Figs. 17 and 18 give a 
good idea of the abnormal inflorescence, the latter figure representing 
a rather advanced though by no means extreme stage of compounding. 
In general it is the lowermost rays of the flower cluster which 
become compound, but there are inflorescences, and perhaps indi- 
vidual plants, in which this is not true. 
The range of variation in the abnormal pedicels is, as shown in 
Figs. 1-16,^ of the two plates, very great. In the earlier work with 
the form I devoted much attention to the attempt to classify the 
various anomalies into logical groups: for example, to distinguish 
between synanthies and the compounding of the flower stalk, and 
between synanthies and the production of an accessory pedicel im- 
mediately below the terminal receptacle. 
^ Schneider, C. K., Illust. Hand. Laubholzk. 465. 1905. 
5 Briot, Rev. Hort. 37: 269. 1866. 
^ Zabel, H., Mitteil. Deutsch. Dend. Ges. 1904; 59-60. 
^ Figs. 1-16 are natural size, Figs. 17-18 twice natural size. 
