62 Maine Agricultural Experiment Station. 19ZU. 



The number of good seeds in the crossed apples is greater 

 than in those which are selfed. 



The causes of self sterility in the apple are external and 

 internal. The external, weather, spraying, insects, and disease, 

 are somewhat within the control of the grower. 



The chief internal cause of sterility is the slowness of 

 growth of the pollen tube in the selfed style as against that in 

 the crossed style. 



Aside from the environmental factors, weather conditions 

 at the blooming period, etc., there is an inborn tendency of 

 certain plants not to produce fruit when fertilized by their own 

 pollen or the pollen of certain varieties within their own species 

 or different species. Among the plants with a well marked 

 tendency in this direction of self sterility and cross sterility is 

 the apple. The tendency of certain of the more common varie- 

 ties of this species is apparently quite distinct and well marked, 

 within other varieties the trees seem to self fertilize readily 

 with their own pollen. It is of especial importance to the prac- 

 tical grower here in Maine to know what varieties are self fer- 

 tile and what varieties should have other varieties near by so 

 that the necessary crossing may take place. It is further of 

 importance to know what varieties of those that must be crossed 

 to produce a fair yield, should be planted together so that the 

 best yield and quality of fruit may be obtained. A large amount 

 of time has been devoted to the solution of this problem- by the 

 staff of the Biological Laboratory of the Maine Station. 



Materials and Methods. 



The apple orchards and scattering apple trees of Highmoor 

 Farm total to approximately 3000 trees. When the grafts are 

 included there are about 25 different varieties represented with- 

 in this group of 3000 trees. The experiments herein described 

 include 16 of these varieties. Controlled crosses have been 

 made between these varieties. The apples resulting from these. 

 crosses were measured. The number of good seed and the 

 number of poor seed were determined for each cross. The ger- 

 mination of these seeds when planted out doors in a cold frame 



