392 



HORTICULTURE 



September 11, 1909 



the newly emasculated flower. There 

 are as many methods of applying pol- 

 len as there are plant breeders, but 

 the usual way is to apply the collected 

 pollen with a camel's hair brush. I 

 have obtained fine results by dipping 

 the stigma into the pollen that has 

 been collected on soft paper. In case 

 that the pollen is to be applied one or 

 two days later than the emasculation, 

 the stigma should be securely covered 

 with a small paper or linen bag, in 

 order to keep insects away. Then 

 when the pollen has been applied 

 cover again as before for a day or 

 two. Then remove bags and the work 

 is done. The pollen grains will be 

 dissolved by the pistil and the male 

 nucleus follow the channel of the 

 stile down to the ovary and fertilize 

 the ovules. Until this is done the 

 young fruit will not set. If the pollen 

 has been applied in sufficient quanti- 

 ties, and the cross not too radical, 

 most or quite all the seeds will de- 

 velop, in which case the fruit will be 

 better, and the breeder will have a 

 much better chance to get seedlings. 

 Apparently, a few fruits have been de- 

 veloped that need no fertilization of 

 flowers, — for instance the seedless 

 orange. I have not studied the mor- 

 phology of this fruit, and cannot dis- 

 cuss it. Generally, the fruit depends 

 upon the development of the seed, and 

 the development of the seed depends 

 upon the fertilization of the ovary 

 with pollen, and this depends in turn 

 on the successful fusion of the nuclei 

 of the ovule with the pollen grains. 



Effects of Crossing. 



One can say without fear of suc- 

 cessful contradiction that crossing 

 when properly applied will be found 

 a means of combining desirable quali- 

 ties in two or more fruits sufficiently 

 related to admit of crossing at all. 

 If the Russet apple is to a great ex- 

 tent disease resistant, and the Bald- 

 win a large, beautiful red apple, but 

 somewhat susceptible to certain dis- 

 eases, we may combine these two 

 qualities by crossing. This of course 

 will entail upon the breed a great deal 

 of detail, for the dominant and reces- 

 sive characters must be studied and 

 the strength and breadth of the allelo- 

 morphic pairs known. For instance, 

 if red and the lack of red or green 

 constitute one of the allelomorphic 

 pairs in a cross between the Baldwin 

 and the Russet apples, the breeder 

 must take careful notes as to which 

 one of these pairs dominate in the 

 first generation of crosses, and he 

 must further calculate what percent 

 of the total area of the apples in the 

 second generation or F2 generation 

 will be red, if he would secure the 

 desired results in the minimum time. 



Another good effect in crossing, is 

 the infusion of new lite into the off- 

 springs. They seem to be more vigor- 

 ous and hardy. An illustration of 

 this is found in the cross between the 

 Newton apple and several other va- 

 rieties. In every case the offspring 

 was far more vigorous and a more 

 salable fruit. It might be claimed 

 that all the qualities were not im- 

 proved in any specific case, but on the 

 •other hand, the size and appearance 

 were greatly improved without ex- 

 ception. Where the apples were 

 crossed, they showed increase in 

 weight and in the number of seeds 

 -developed. 



The Spitzbergen apple is almost 

 self-sterile, being able to set only 

 about 3 per cent, of its own fruit. 

 When crossed with Ottley, Baldwin 

 and other varieties it was much im- 

 proved. The few self-fertilized Spitz- 

 bergens were small, ill-shapen, and 

 otherwise objectionable. To what ex- 

 tent then are self-sterile apples im- 

 proved by cross fertilization? In each 

 of the above cases, they were greatly 

 Improved, and the conclusion among 

 horticulturists is that this rule is al- 

 most if not quite universal, that where 

 apples are found to be self-sterile, the 

 few individual fruits that may prove 

 self-fertile are not as good and strong 

 as those on the same trees that are 

 obtained by cross pollination. 



Is self-sterility brought about by 

 cross fertilization? There is some 

 reason to believe that where plants 

 are continually crossed for effect, they 

 eventually come to depend for fer- 

 tilization on foreign pollen. Many 

 cases of self-sterile horticultural 

 plants have been brought by crossing 

 foreign on native fruits. However, in 

 this way we have been able to pro- 

 duce much of our best fruit. As we 

 come from the distant past when most 

 of our varieties of fruits were foreign, 

 to the present when most of them 

 are native or American-produced and 

 American-named, we cannot fail to 

 notice the activity of growers and the 

 eagerness of speculators to adopt the 

 promising new fruits. The foreign 

 element has continued to pour into 

 most of our horticultural plants. 

 Among the last of these is the 'New 

 Hybrid Fruits' at the South Dakota 

 Experiment Station published in bul- 

 letin 108,. May 1908. Our native wild 

 fruits seem to be susceptible to con- 

 siderable development when crossed 

 on good foreign fruits. The sand 

 cherry on the Chinese apricot is a 

 good illustration of this. Another is 

 our native plum on the Chinese 

 apricot. By means of these crosses, 

 foreign fruits are easily adapted to our 

 soil and environment, as well as cli- 

 matic conditions and at the same time 

 our native fruits are being greatly im- 

 proved. 



Limits of Crossing. 



There are bad as well as good ef- 

 fects from cross pollination, and my 

 paper would not be complete without 

 devoting some space to this phase of 

 the subject. Bailey has said: "Cross- 

 ing is useful as a means of originating 

 new forms adapted to man's special 

 uses and also as a means of revitaliz- 

 ing the offspring by providing new 

 combinations of characters which may 

 better enable the individual to com- 

 pete in the struggle for existence; 

 but there are limits beyond which 

 clossing is useful neither to the spe- 

 cies nor to man." What are these 

 limitations? To what extent may 

 crossing be made to prove profitable, 

 and when does it work injury to the 

 plant? If the cross ceases to be use- 

 ful to the plant shall we consider it 

 wise to continue crossing for benefits 

 to man? Artificial or cultivated plants 

 have very few of the natural factors 

 of limitation to work under. They 

 have no struggle for existence. Man 

 does their struggling. The weed is 

 hardier and would get the better of 

 the cultivated plant, but man steps in 

 and destroys the weed. In two ways, 

 man aids cultivated plants: by selec- 



tion and cultivation, and by destroy- 

 ing their enemies. Therefore the 

 great consideration is improvement. 

 Making something better, along defi- 

 nite lines and for specific purposes. 



When selection is not sulficient to 

 produce the required effect in the im- 

 provement of plants, crossing varieties 

 is resorted to. When the end in view 

 has been attained without too much 

 sacrifice, the breeder is fortunate. 

 Sometimes self-sterility is so pro- 

 nounced that the desired fruit will 

 have to be abandoned, the latter ac- 

 tion dependent on accessibility to or 

 our possibility of growing the desired 

 pollen with which to fertilize the ster- 

 ile varieties. 



This leads to a consideration of the 

 causes of self-sterility in orchards. 

 One authority says that the cause of 

 self-sterility is that the pollen of a va- 

 riety is unable to fertilize the pistils 

 of that same variety. But this is only 

 half of the truth. The other part of 

 the question might with propriety be 

 asked: Why will the pollen not fer- 

 tilize the pistils of the same variety? 

 Cannon has come nearer the truth in 

 his discussion — the cytological aspects 

 of breeding. In order for the pollen 

 to fertilize the ovules without a radi- 

 car disturbance, there must be a com- 

 mon number of chromosomes and con- 

 sequently a like reduction of chromo- 

 somes in the sperm and ovum. The 

 spermatocyte must be the morpho- 

 logical equivalent of the oocyte. There 

 is then a possibility that part of the 

 offsprings of certain crosses — I might 

 say radical crosses, are normal and 

 part abnormal. The normal adhere to 

 the original method of cell division, 

 and the latter do not. In the normal 

 development, the sperm and ovum 

 had an equal number of ch'romosomes, 

 in which case the spindle would be 

 exactly like that in the parent types. 

 In the abnormal development we may 

 have direct nuclear multiplication, or 

 amitosis, and consequently a general 

 biological or morphological difference. 

 The last or abnormal difference, Can- 

 non says may be the cause of self- 

 sterility, and the former or normal 

 development the cause for fertility of 

 self-fertility. In order to successfully 

 answer the question, there must be a 

 combined study of cytology and field 

 experiments. The whole matter is a 

 problem of morphology, and without 

 making cytology the basis of an in- 

 vestigation of this problem, one can- 

 not hope to unravel the fundamental 

 truth. 



Suggestions. 

 It is suggested tliat, in as much as 

 there are so many institutions in the 

 country that exist solely for research 

 work and experimental investigations, 

 horticulturists follow well tried meth- 

 ods, and refer new problems to such 

 institutions. Practical crossing and 

 not theoretical breeding is the only 

 safe rule for the ordinary horticul- 

 turist. The work in cross pollination 

 should be principally with self-sterile 

 varieties, and the pollen used should 

 be from some thoroughly tested varie- 

 ties. Or, if foreign pollen is known 

 to work well with self-fertile varieties, 

 no risk will be run by such practice. 



References: Bailey, Survival of the Un- 

 like. Cannon, C.vtologlcal Aspects of 

 Breeding. Bulletin, 132 Maine Station. 

 Bulletin, 104 Oregon Station. Bulletin, 181 

 Cornell Station. Wilson, The Cell. Bulle- 

 tin, 108 South Dakota Station. 



