1916] Goodspeed-Ayres: Sterility of Nicotiana Hybrids 279 



Table 2, below, gives the results of one of a number of attempts 

 to measure the reaction of the parental pollen to various artificial 

 germinating fluids. Hanging-drop cultures of the pollen were made 

 in tap water and in 10 per cent solutions of levulose, dextrose, and 

 maltose. After four hours in a moist chamber at 20"^ C. the average 

 length of the pollen-tubes was determined. Twenty-five measurements 

 taken at random in the preparation gave, in each case, the average 

 amount of growth. The length of the pollen-tubes is stated in divisions 

 of the eyepiece micrometer with the 2/3 objective. 



From tbe results given in table 2 it is plain that the pollen of the 

 two species used reacts differently to the same culture medium. The 

 pollen of N. sylvestris germinates rather poorly and the pollen-tubes 

 grow slowly in tap water, as contrasted with the high percentage of 

 germination and the rapid growth of the pollen and pollen-tubes of 

 N. Tab. var. macropliylla in the same culture medium. Almost 

 exactly the reverse is true of the behavior of the two types of pollen 

 in maltose, while in levulose the pollen of N. Tab. var. macropliylla 

 will not germinate at all and the pollen of .Y. sylvestris shows very 

 slight germination and feeble growth of pollen-tubes. The fact that 

 specific chemical substances appeared to exert a stimulating effect upon 

 the germination and growth of the pollen on the parents led to the 

 use of a variety of substances in the hope of finding one which would 

 induce germination of the hybrid pollen of normal appearance. 

 Numerous .sugars, dilute acids and various nutritive .substances in 

 different concentrations were u.secl as culture media. No .success 

 attended these various efforts, and it seems certain that it is not the 

 absence of specific chemical .substances in natural stigmatic secretions 

 Mliich accounts for the failure of the F, pollen normal in appearance 

 to germinate in its own stigmatic fluid or in that of its parents. 



These experiments on pollen geniiination as a phase of tbe general 

 investigation wero undertaken a number of years ago, and our atten- 

 tion has more recently been directed to various nutrition experiments 

 which are to be descrilicd in what follows. In our efforts to bring about 

 the germination of !!ic a])]iar(»ntly iioniinl ])ollen of the F, hyhfid 

 we were gni(l('<l i)i-iin;ii"ily by 1hc oldci' concc^ption of tlie iiii]iortant 



