CHAPTEE XXXIX. 



EXPERIMENTAL WORK ON THE SELF-STERILITY OF THE APPLE. 



By W. H. Alderman, University of West Virginia. 

 (Abstracted by C.H.H. from the Proceedings of the American Society of Horticultural Science, 1917). 



The fact has been noticed that in spite 

 of apples and pears being generally self- 

 sterile, there are reasonably productive 

 orchards where the plantings are made 

 up of a single variety, notably is this the 

 case in " Rome Beauty " and " Baldwin " 

 apples. In order to check whether there 

 were any possible error in the usual 

 methods of trial, experiments were made 

 to consider and ascertain the following 

 facts : — (1) Whether the conditions within 

 paper sacks are abnormal from the stand- 

 point of temperature and humidity; (2) 

 individual flowers or clusters of flowers 

 have been studied without regard to the 

 rest of the tree, whereas in orchard con- 

 ditions the tree is a unit; (3) the emascu- 

 lation of bloom produces decidedly 

 abnormal conditions — do these affect the 

 results in any unknown way 1 ; and (4) 

 whether pollen from other trees of the 

 same variety is more effective than from 

 flowers on the same tree, even though a 

 single flower or single tree is shown to be 

 self-sterile within itself. 



I. In a comparative test on some 20,000 

 blossoms of the setting of fruit on trees 

 enclosed in muslin frames, and blossoms 

 enclosed in paper bags, to the surprise of 

 the experimenters the paper sacks gave 

 the better results, as far as per cent, of 

 set was concerned, and at least the fact 

 is established that the bags do not hinder 

 the setting of fruit. 



In these various trials about 150,000 

 flowers have been pollinated and records 

 kept. 



II. The summary of 3 years' work with 

 Rome Beauty, York Imperial, and 

 Wagener is that there is no advantage 

 gained by pollinating a tree with pollen 

 from another tree of the same variety over 

 using pollen of the same tree. It is in- 



teresting to observe that Rome Beauty 

 does not normally set as large a per cent, 

 of its blossom as do Wagener or York 

 Imperial. Under orchard conditions, and 

 open to free pollination by several 

 varieties, Rome Beauty set 4.46 per cent, 

 of its blossoms, whereas York Imperial 

 set 7.87 per cent., and Wagener 8.5 per 

 cent. From this it is clear that one may 

 not judge the relative sterility of two 

 varieties by direct comparison of percent- 

 age of fruit set upon each, but rather by 

 comparison of such set of fruit to the 

 normal set of the variety. In the same 

 way the efficiency of a mutual pollenizer 

 may not be judged by a direct comparison 

 of its effects upon two varieties, but 

 rather by a comparison to the normal set 

 of each. A study of the results of pollen- 

 ation trials show clearly that while none 

 of the varieties are entirely self-sterile, 

 they are greatly benefited by cross fei'tili- 

 sation ; thus in the case of Rome Beauty 

 the percentage of set was increased three- 

 and-a-half times, York Imperial fourteen 

 times, and Wagener seven times. This 

 advantage is further greatly augmented 

 when we note that the size of the 

 individual fruits was increased by cross- 

 ing. The increase in the case of Rome 

 Beauty was 27.8 per cent., and in York 

 Imperial 42.7 per cent over the size of 

 the self-pollinated fruits. 



III. For 2 years experiments were made 

 to ascertain the effect of emasculation 

 upon the setting of the fruit ; it was found 

 that the set of fruit under emasculation 

 conditions was more than double that 

 where no emasculation was practised. It 

 seems to make no difference in the results 

 if the entire calyx and corolla are removed, 

 merely the corolla, or if both are left 

 practically intact, and only the anthers 



