CONTRIBUTIONS FROM THE WISLEY LABORATORY. 617 



to fruit may be too easily regarded as due to this cause. That lack 

 of efficient pollination is one prolific cause of unfruitfulness there is 

 not a shadow of doubt ; but the weather, both of the year before and 

 of the flowering season, is a potent and very complex factor. The 

 extreme conditions of weather prevailing at the season of flowering are 

 mitigated by the enclosure of the flowers in paper bags ; but their 

 effects are not entirely removed, for we have had flowers killed by frost 

 even after such enclosure. Birds, fungi, insects of various kinds, and 

 accidents account for still further failures ; and no doubt the condition 

 of the tree — an expression that connotes a large variety of circum- 

 stances — is answerable for other failures, and accounts for some of the 

 apparently contradictory results recorded below. 



An orchard-house has been erected at Wisley to enable us to carry 

 out further experiments, with the object of eliminating some of these 

 disturbing factors, and we propose to postpone the full discussion of 

 the results till some of these further experiments have been carried out. 

 Certain other aspects of the questions, e.g., the relative efficiency of the 

 pollen of different varieties of apples in promoting fruitfulness in 

 another variety, and the necessary conditions for securing efficient 

 pollination, are also being considered and will be reported on in due 

 course. Pears are also being experimented with. 



As full discussion of the results is postponed, we have made no 

 attempt here to correlate our findings with those obtained in America 

 and elsewhere. 



It is perhaps well to say again that the negative results obtained, and 

 shown in Table II. , although suggestive, must not be taken as conclusive 

 evidence of self-sterility. Further, it is not yet clear that a variety 

 behaves in the same way in this respect over the whole of its area of 

 distribution, nor that all the plants of one variety are precisely 

 similar, with regard to this character, though they probably are, 

 other things being equal. 



Definition of Terms. 



The point that many apples are able to form fruit without the aid 

 of foreign pollen is clearly brought out in the following table, while 

 most appear to be sterile with their own pollen. 



I have previously * drawn attention to the fact that the term self- 

 fertility in apples and pears is loosely applied to two classes of 

 phenomena: .in the restricted sense, it implies that viable seed is 

 produced ; in the wider sense— the sense that alone concerns the 

 producer of fruit — it means that the fleshy envelope of the fruit is formed 

 while there may or may not be seed enclosed within it. For the latter 

 class, I propose the term self-fruitful instead of self-fertile, restricting 

 the latter term to those cases where seed is produced. No attempt has 

 been made to show which varieties are self-fertile in this sense in the 

 Table. The third term, self-sterile, means that fruit formation is not 

 induced by the action of the pollen of the same variety. 



* Chittenden, F. J., I, c, antep. 350. 



