48 



SCIENTIFIC AGRICULTURE 



October 



to induce fruitfuliiess uiider different con- 

 ditions. 



Wliere the trees are, or should be, in 

 full bearing, four conditions may exist : 

 The tree may be non-blossoming, i.e., pro- 

 ducing very short spur growth j it may be 

 blossoming but non-fruiting, i.e., producing 

 only weak blossoming spurs; it may be 

 biennial bearing; or it may be annual 

 bearing. 



In the first two instances vegetative 

 vigor is evidently at a low ebb and early 

 applications of nitrates and early cultiva- 

 tion should induce longer spur growth with 

 resultant fruitfuliiess. Or the same end 

 could probably be reached by cutting back 

 lightly in the vicinity of fruit spurs. 



Where the tree is biennial bearing, treat- 

 ment should commence in the off j'ear. 

 During this year if left to its own devices 

 an over abundance, of spurs will fall into 

 the V2-"ich and 3/16-iiicli class; these will 

 be blossom buds which will blossom and 

 fruit or blossom and not fruit. If a per- 

 f-entage of these can be induced to become 

 over-vegetative it will reduce the propor- 

 tion blooming the following year and those 

 spurs which have become over-vegetative 

 during the off year will form blossom buds 

 during the following season and fruit the 

 season after. 



Here again the application of nitrates 

 might have some effect if applied early 

 enough, but probably a light pruning 

 would be more advantageous. The prun- 

 ing in tliis case should consist of light 

 cuts made in tlie vicinity of the fruit spurs, 

 and should be distributed over the entire 

 tree as pruning is largely local in its ef- 

 fect. Tlie removal of a few large limbs 

 will not serve the purpose. It should l)e 

 done before the buds bi-eak. The import- 

 ance of the admission ol" sunlight to all 

 parts of the tree should be pointed out. "SVe 

 have seen that carbohydrates are essential 

 to fruitfulnoss as well as nitrogen; also 

 tliat carbohydrates ai"e stored very close 

 to their point of manufacture; that the 

 removal of leaves from spurs prevented 

 blossom bud formation on that s])ur with- 

 out inhibiting blossom bud formation on 

 other spurs cf the same tree not so treated; 

 that consequently we are led to conclude 

 that spurs, branches, or local parts of a 

 tree act largely as individuals and it should 



be added that for carbohydrate formation 

 sunlight is necessary. 



Considering, therefore, the previous 

 paragrapli it will readily be seen that light 

 must be admitted to all parts of the tree 

 if the older, spurs are to function properly, 

 for these older spurs far down the tree 

 cannot draw on the leaves at the top for 

 their carbohydrate supply. 



Another phase of horticultural research 

 upon which we are slowly gaining know- 

 ledge is the question of pollination. To 

 obtain fruit it is not only necessary for 

 pollen to be produced, but it is necessary 

 that the pollen be capable of germination 

 and ultimatel^• must reach the ovary of the 

 plant in time to bring about germination. 

 Dorsey in his researches on pollination of 

 the plum has shown us that the rate of 

 pollen tube growth is a factor of great im- 

 portance. He has demonstrated that in so 

 far as the plum is concerned the abscission 

 of the style takes place fairly constantly 

 and is not hastened or delayed to any great 

 extend by the changes of weather. Fur- 

 ther fliat wet weather may prevent the 

 opening of the pollen sacs or in scientific 

 parlance delay dehiscence, and that even 

 under favourable conditions the rate of 

 l)ollen tube growth in the plum is so close 

 ill length of time to that of the effective 

 life of the style that a delay of a day or 

 two may prevent the pollen tube from 

 reaching the ovary before abscission of the 

 style has taken place. 



As pollen liberation may be delayed by 

 weatlier and as subsequent growth of the 

 ])ollen tube after dehiscence is regulated 

 largely by weather conditions the factor 

 of safety in blossom pollination is rather 

 small. 



There is a problem here which may have 

 an \dtimate bearing on our future pomo- 

 logy. Is there an appreciable difference 

 in the rate of pollen tube growth of dif- 

 ferent varieties of the same species? If 

 so, and we can select as ]->ollinizers those 

 which exhibit a very rejiid rate of pollen 

 tube growth, we may go a long way toward 

 solving some of our ]iresent difficulties of 

 light sets where a full bloom is in evidence. 



Not only is it possible that there is a 

 variation in the rate of pollen tube growth 

 but there may also be a difference in style 

 length. This latter, if found of value. l)ein£r 



