i6 
NOTES ON PLUM CULTURE. 
been made regarding other varieties, but the experiments 
carried on by Professor Waugh of Vermont, in 1896 and 1897, 
indicate that the actual extent of self-sterility among varie- 
ties of plums, has by no means been appreciated or even 
suspected. His tabulation shows that of 6,428 blossoms cov- 
ered, on 56 varieties, representing all classes of plums, only 
five produced fruits, and from the experiments he draws the 
conclusion that “For all practical purposes, all classes and va- 
rieties of native plums may be regarded as absolutely self- 
sterile.” It is possible that these results might vary with 
different seasons and in different localities, but making due 
allowance for possible variations, the results are startling 
enough to warrant the attention of plum growers every- 
where. The cause of this sterility appears to lie largely in 
the inefficiency of the pollen of the flowers of a plant upon 
the stigmas of the flowers of the same plant. It lies in a 
condition known to exist among many wild as well as culti- 
vated plants. One of nature’s provisions for securing cross- 
fertilization, and the plants come under the recognized 
Knight’s Law that “Nature intended that a sexual inter- 
course should take place between neighboring plants of the 
same species.” 
Self-sterility may also be due in some degree to imper- 
fect pistils, the cause for which must be sought in some 
physiological weakness of the tree, such as might be brought 
about by the work of insects or disease, or from a feeble 
condition following the production of a phenomenally heavy 
crop of fruit. Or it may be due to unfavorable weather con- 
ditions prevailing at blooming time. 
Recognizing, then, the existence of self-sterility among 
plums, the aim should be to so associate the varieties that one 
may supply pollen for the other. No data is at hand to 
warrant any definite statement as to what varieties are es- 
pecially adapted to the fertilization of certain other varie- 
ties, but it is perfectly plain that to be of use to each other 
the varieties must bloom at the same time. 
The varieties now available from which to choose show 
a rather wide range in blooming period; some bloom to- 
gether, some finish before others begin and some overlap. 
All are much influenced by the weather at the time, and 
this may vary greatly in different years, not only in the ap- 
pearance of the first flowers, but in the length of the bloom- 
ing period. While irregularities may occur from one sea- 
son to another, it is probable that the relative periods of the 
different varieties will remain much the same. For the con- 
venience of those who may be interested, and also as a stim- 
