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•.".IIY _I3 CROSS F0LLI::ATI0F NECES3j\HY? 



Tliis question is often asked by inquisitive fruit grwrers as v/ell as students. 

 It can be "briefly arisr;ered by stating that the constitution of sotac fruit plants 

 is such as to malce self-fertilization impossible. Sorae varieties of apple such as 

 Gravenstein produce only a very small ainount of viable pollenB This is because 

 such varieties have an uneven number of chroinosomes in th.eir cells. As a result, 

 when cell di\'ision takes place during the fonuatinn of pollen,, raaiiy pollen grains 

 fail to receive their full quota of chro:AOsomes r Consequently, tl:ose pollen grains 

 do not mature properly and the result is many abortive pollen grains, v:Idch fail 

 to geminate siriilarly as do the shrivelled seeds one sometimes finds in an apple, 

 Naturally, one v/ould not choose such a variety as a pollenizer for itself or exiy 

 other variety, 



IIoa';ever, another condition laiovm as self- incompatibility exists in most of 

 our apple, pear, pliun and sv/eet ch&rrj'- varieties. In this case the varieties have 

 an even nujaber of chromosomes. Each pollen grain receives its noiTial quota of half 

 of them' and develops into a good plump grain which v;ill gen-ainate a:ad gi'ow. 

 However, it villi germinate and grov; only in the blossom of e^iother variety, — not 

 in a blossom of its mai variety — because it carries a genetic factor v;hich 

 inhibits the grovrth of the pollen tube dovm tjirough a pistil of like genetic 

 mal:e-up. In this caso, like ropels like, so \'^ry little, if any, fn;it is produced 

 unless a good pollenizer is nearby. 



In the case of sv;eet cherries there are many varieties v:hich not only are 

 self-incompatible ; but also cross incompatible v/ith several other variotios. 

 Fortunately, this is not a coriimon situation in apples. On the ether hand, most 

 peach and seme cherry varieties vdll set fruit by themselves because nature did 

 not endavr them r/ith thi-^ peculiar type of her3dity» 



Self-incompatibility is not peculiar to fruit plants. As a matter of fact 

 it is found also in jcv'?ral vc-gotatles, flor-ers, and othev crops.. It may be of 

 interest to note that the first case of it vras discovered in the wild mullcn 

 nearly tare hundred yoars ago by a botanist v;ho vw.s not; at all intez-estcd in helping 

 fruit grwrers to get a better set in seasons such as the past spring, 



— A, P, French 



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SOIL ^riJITY ; ITS CAUSES, EFFECTS J^ID CURBS 



Soils naturally, contain eitiier insoluble clay or hunic acids, In'most 

 productive soils these soil acids are combined with bases such as lime, magnesia 

 and potash. Soils became progressively more acid and less productive as these 

 bases are lost from the soil by leaching or by having been ■absorbed. by the crops. 

 Many agricultural practices speed up the losses of tiioso bases. In orchard soils, 

 dusting sulfur and nitrogen fertilizers are particularly effective in increasing 

 the losses of these bases because the sulfur produces sulfuric acid and nitrogen 

 fertilizers produce nitric acid in the soils. Both of these strong acids increase 

 the solubility of the bases in the soil v;ater and cause their more rapid loss as a 

 result of Icaciiing or cropping. 



There are several direct effects on the productivity of soils v;hich I'esult 

 from the loss of bases. Calcium, magn-osiura and potassium bccomo limiting factors 

 in plant growth because of their r--^!lative scarcity rather thcji from the inability 

 of plants to secure cither of those elements from the acid soil. Calcium, magnes- 

 ium and potassium are kna-m to be quite available for absorption by plants vrhcn 

 thej' ore pr sent in acid soils. Plants have a tendency to absorb a constant total 



