UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



BOTANY 



Vol. 5, No. 13, pp. 429-434 August 10, 1918 



CONTROLLED POLLINATION IN NICOTIAN A 



BY 



THOMAS HARPER GOODSPEED and PIRIE DAVIDSON 



In the course of the breeding experiments with Nicotiana carried on 

 in the Botanical Garden of the University of California the question 

 has arisen on a number of occasions and in a variety of connections as 

 to the relation in this genus between the number of pollen grains 

 applied to the stigma, the number of fertilizations accomplished and, 

 finally, the number of seeds resulting. In the case of the F^ Tabacum- 

 sylvestris hybrids, for example, it has been shown that a few ovules 

 capable of fertilization and the production of viable seeds are matured, 

 and it has seemed possible that at least a corresponding percentage of 

 normal pollen grains are produced. In field practice it is impossible, 

 however, to obtain selfed seed of these hybrids even when the stigmas 

 are artificially close, or self-pollinated with a considerable excess of 

 pollen ; the flowers thus treated falling after some days just as those 

 allowed to pollinate themselves naturally under bag. In this connec- 

 tion it would be of interest to know whether in self-fertile species a 

 relatively large excess of normal pollen is necessary to accomplish the 

 fertilization of a relatively small number of ovules and whether the 

 fertilization of three or four ovules is sufficient to inhibit the abscission 

 which follows entire absence of pollination. Again, branching pollen 

 tubes have been observed in a number of species of Nicotiana when 

 the pollen was grown in artificial germinating media. If such 

 branching occurs in the style and is accompanied by a division of 

 male nuclei with the result that more than one ovule is fertilized by 

 a single pollen grain, it would obviously be of importance in the 

 interpretation of F, ratios, etc.^ With these and other points in mind 



1 A cytological examination of a number of the branching pollen tubes gave 

 some evidence that at least chromatin fragments were present in two or more 

 of the branches. This fact might suggest that the abnormal germinating fluid 

 of the pollen cultures was alone responsible for the branching and further 

 resulted in a fragmentation of the initial nuclear material. 



