204 BOTANICAL GAZETTE [APRIL 
should indicate zero for the one absent. In applying the method 
to the plum samples, the results in general did give zero values for 
tartaric. In some cases, however, positive values were obtained, 
and in others even negative values. Since these anomalies 
indicated the presence of some interfering substance, it was found 
necessary to reject.all the data on these two acids; hence they are 
not presented here, although it was deemed well to record this 
failure of the double polarization method on plum juices. 
Experimental data 
CHARACTERISTICS OF ROT.—In table I are listed the varieties of 
plums used, the abbreviations for these varieties used throughout 
this paper, the dates of taking samples, and the length of time 
required for rotting in each case. Probably the same degree of 
.rotting was not obtained in all cases, but the relative rates of 
progress of the fungus attacks are no doubt fairly well indicated 
‘ TABLE J 
SAMPLING DATA FOR VARIETIES OF PLUMS USED 
Stace I, Stace II, Stace III, 
HALF GROWN FULLY GROWN" RIPE 
VARIETIES sa 
TIONS USED Days Days - Days 
Picked | required} Picked | required] Picked | required 
to rot to rot é to.rot 
ee ete b nk Wolf BxXW 
urbank X Wolf 9....... <Wooro July r2 15 Aug. 2 I Aug. 31 ‘s 
Burbank X Wolf 16....... BXW1r6or16} Julyr2| 13 Aug. re 8 Aug. 28 15 
Abundance X Wolf 30... ..|/AX W30 0r30/ July 12 13 oll ocas caniaee eens 
Susceptible 
ompass Jf July 12 9 Aug: tI Aug. 20 12 
Sand Cherry XFormosa.. | SCF July12|} 10 yin : 13 Aug. 11 12 
by the figures. It is clear that the varieties listed by the horti- 
culturists as resistant are considerably more slowly rotted than are 
the susceptible varieties. There is more difference in this respect 
in the earlier than in the later samples. This is in accordance with 
the commonly observed characteristics of fruit diseases, that in 
general they become less resistant as maturity approaches. Because 
of this, the first set of samples was observed more keenly than the 
following ones, and some interesting points were noted. In con- 
nection with the rate of spread of the rot, the time required for 
