38 THE PLUM IN KANSAS. 



ness of pistils and conditions of soil, cultivation, or climate. It should 

 be noted that the same tree varies from year to year. The pistils may 

 be all defective one year, and all sound the next. 



Different varieties vary greatly in the amount of pollen produced. 

 This variation seems also to follow somewhat the specific parentage 

 of the varieties. Thus, plums of the amerlcana grouj) are generally 

 more abundant pollen bearers. The Chickasaw plums are rather 

 weaker pollen bearers, though they seldom show serious deficiency. 

 The Japanese plums are still weaker, while the Marianna is distinctly 

 lacking in the quantity and perhaps also in the quality of pollen pro- 

 duced. A comparison of the several groups as jjollen bearers is made 

 in table 2. 



Table 2. — Compari.^on of Groups 



In the matter of pollen bearing. Figures indicate the number of samples under each rating. 



In connection with any estimates on the point of comparative polli- 

 nating efficiency several things have to be taken into account. In 

 the first place, any estimate of the quantity of pollen borne must nec- 

 essarily be very rough. In the second place, there may be a differ- 

 ence in the quality of the pollen. I have examined some samples in 

 which many imperfect grains could be noted with a low-power lens. 

 In other samjjles apparently well-formed grains would fail to respond 

 to micro-chemical tests for protoplasm ( Millon's reagent), leaving a 

 strong presumption against their ability of fecundating the ovules. 

 But above all this, the pistils of many varieties appear to have a pro- 

 nounced selective ability, whereby they refuse certain pollen while 

 receiving readily pollen from some other source. Our knowledge is 

 very imperfect on all these points, but we know enough to make us 

 very cautious how we dogmatize about this question. Much more 

 careful field experii:jientation is needed along these lines. 



In order to gain some evidence on the point raised by Professor 

 Goff and others, that the severe northern climates are accountable for 

 much of the defectiveness of plum pistils, table 3 has been pre- 

 pared. 



The different locations are arranged in the table, as far as practica- 

 ble, in the order of their geographical latitude. The testimony of 

 the table is not very emphatic, it is true, but it does not sustain the 



