BOTTLE GRAFTING 



A. F. ])LAKESLEE and M. E. P'arnham 

 Station for Expcr'nncutal Evolution, Cold Spring Harbor, Long Island. 



IT is well known that plant hybrids 

 are usually unable to breed true 

 when })ropagate(l by seed, but for- 

 tunately, in the majority of cases a 

 desirable plant can be multiplied by 

 veg'etative means. Thus most of our 

 fruit trees and our various named 

 varieties of roses, tulips, dahlias, 

 potatoes and many other plants are 

 kei)t true to type by the processes of 

 budding, grafting or propagating by 

 cuttings or by vegetative means of re- 

 production such as bulbs, roots and 

 tubers. By the chance union of Men- 

 delian factors in hybridization many 

 combinations of characters are possi- 

 ble, and it is usually the rare combi- 

 nations which give us our choicest 

 varieties. These choice varieties are 

 usually highly complex hybrids, and 

 in consequence the mixture of factors 

 which they contain segregate and pro- 

 duce new combinations in the forma- 

 tion of pollen and tgg cells. This is 

 the reason that they cannot breed 

 true by seed. Seedless methods of 

 multiplication are of value not only 

 to the practical plant grovi^er but to 

 the plant geneticist as well, who fre- 

 quently wishes to carry over individual 

 jilants from one season to the next in 

 order to use them in his breeding ex- 

 periments. 



In our work with the Jimson Weed, 

 for example, there are many forms 

 which, when propagated by seed, give 

 rise to only a small percentage of off- 

 spring like the parental type. Others 

 like our Haploid and Triploid Daturas 

 (with one-half and one and one-half 

 times the normal number of chromo- 

 somes respectively) cannot ordinarily be 

 expected to produce any seedlings like 

 themselves, and therefore can be car- 

 ried over only by vegetative propaga- 

 tion. Grafting has been found rather 



difficult with material which has been 

 checked in its vegetative growth both 

 by fruiting and by the low tempera- 

 ture encountered toward the end of the 

 growing season. If the grafted plants 

 were kept too moist they would tend 

 to rot. If the surrounding air were 

 not moist enough, they would dry out 

 and no union would be formed be- 

 tween scion and stock. 



To obviate the difficulties which 

 have been enumerated the idea oc- 

 curred to us of keeping the scion sup- 

 plied with water during the formation 

 of callus by immersing the base of the 

 scion in a bottle of water. Such bottle 

 grafts have been eminently successful 

 and we are now able to graft readily 

 slow growing forms with which we 

 were formerly rarely successful. We 

 have grafted even albino seed- 

 lings which had not yet shown any 

 true leaves. The process in bottle 

 grafting is relatively simple. Almost 

 any method of grafting can be used, 

 provided the base of the scion is left 

 free for immersion in a bottle of 

 water. The conducting foot should be 

 long enough and project sufficiently to 

 prevent capillary water from wetting 

 the place of junction. We have usually 

 cut the end of the stock to form a 

 wedge which has been inserted into a 

 cleft in the scion. In about two weeks 

 a union is made and the wrapping of 

 raffia may be removed. 



The accompanying photograph (Fig. 

 12) shows various stages in bottle 

 grafting. At the left is a purple- 

 stemmed stock upon which a green- 

 stemmed scion has just been grafted. 

 The base of the latter may be seen in- 

 serted in a small bottle of water which 

 is held to a stake by a rubber band. 

 The pot in the middle contains a stock 

 and scion which were similarlv grafted 



171 



