12 Journal of Agriculture, Victoria. [lo Jan., I9Ii_ 



in the pistil tubes, except in cases such as the sudden dying off of the 

 stigma as, for instance, the Marie Louise pear, before the pollen was ripe. 

 This is not so noticeable in other kinds, but it occurs to some extent." 



Thus it is obvious that, although in some rare cases there may be an 

 underlying cause of sterility or partial sterility owing to some malforma- 

 tion of the reproductive organs of the flower, speaking generally, there 

 is not enough irregularity here to warrant our hxing it as a common cause 

 of the trouble. 



In looking elsewhere for the cause one is struck with the fact that 

 most of the kinds classed as " shy " or " rion " bearers are usually those 

 growing uprightly and vigorously (therefore densely) such as Kieffer's 

 Hybrid pear and Northern Spy apple, or those producing an over- 

 abundant number of spurs, and consequent amount of blossom, as in the 

 case of Winter Nelis pear, Coe's Golden Drop plum, and Early Purple 

 Guigne cherry. It is a well-established fact that upright and vigorous 

 growth on the part of a tree is diametrically opposed to fruitfulness, but 

 in the case of the Kieffer pear it cannot be said that it does not make the 

 attempt to bear, for it generally blossoms heavily. Therefore, it would 

 appear that this over- abundant blossoming on the part of several \arieties 

 may be a predisposing cause to sterility by weakening the pollen to the 

 extent that it becomes impotent upon its own pistils. 



Inspector Davey, of Geelong, states — " I think trees exhaust themselves 

 when they have a very profuse show of blossom. This has been very 

 marked this season in Winter Xelis pear and Coe's Golden Drop plum, 

 both of which trees were all blossom, and yet both have set badly. This 

 may be caused by each of the flowers trying to set fruit, and also by the 

 tree being unable to feed all of them. They therefore abort because^ 

 their struggle for existence is so even. Sometimes, when a flower is 

 slightly more favourably situated, it sets and then we have a tree carry- 

 ing a few solitary fruits." 



There is also another aspect of the question, and that is the fact that 

 some trees, although there may be nothing abnormal in their habit of 

 growth or spur-production, may be self -sterile. Bailey says in his Survival 

 of the Unlike, p. 247 — 



Since the demonstration of the value of sprays for exterminating the insect ani 

 fungus enemies of fruits the most ihiportant advance in American pomology is the 

 discovery that some varieties of fruit are unable to fertilize themselves. 



And on p. 349 the same authority writes — 



The j)istil or seed-bearing member refuses to accept the pollen from the same 

 flower or even from any flower on the same plant ; or, to transpose the statement, the 

 pollen is impotent upon its own sisterhood of pistils. 



In the case of trees of good bearing varieties proving to be barren the 

 cause is likely to be hereditary. Probably, the tree, from which the ones 

 in question were worked, was sterile or partly so. Therefore, all the 

 trees produced by buds or grafts taken from the original one would re- 

 produce its characters, the law that "like begets like" being very aptly 

 illustrated. We may thus summarize the position as to the primary causes 

 of sterility as follows : — 



1. Imperfection of structural arrangement of blossom. 



2. Unfruitful habit of growth and over-production of fruit spurs 



and blossom. 



3. Natural impotency of pollen. 



4. Working by buds or grafts taken from sterile or partly sterile- 



trees. 



