lyi^] Goodspeed-Ayrcs: Sterility of Nicotiaua Hybrids 277 



tives, since every effort was made to supply abnormally large quantities 

 of pollen on the stigmatie surfaces in hand pollinations. Pending the 

 results of the pollen germination studies we did not attempt to isolate 

 numbers of the grains of normal appearance for pollination. It might 

 here be mentioned that the parent species have throughout exhibited 

 a rather remarkable tendency to mature viable seeds under unfavor- 

 able conditions accompanying pollination. Thus, in self or cross- 

 pollination old pollen, overmature pistils and to some extent premature 

 pollination (cf. Hartley, 1902) seem to have relatively little influence 

 upon the seeding qualities of a flower of the parents. 



The various facts mentioned led to the experiments w^hich are 

 described in what follows. Of the various F^ hybrids between N. 

 Tahacum varieties and N. sylvestris which we have had under culti- 

 vation, only that one involving N. Tab. var. macropliylla (female 

 parent) will be considered in this report. The F^ hybrid N. Tab. 

 var. macropliylla X N. sylvestris is known in our cultures as FjH38, 

 N. Tab. var. macrophylla as 22/07, and N. sylvestris as 69/07. 



Table 1 below details the result of one of a number of similar 

 experiments on the germination of the pollen of F^HSS and its parents 

 in the three natural stigmatie fluids contained in parent and hybrid 

 flowers. The stigmatie secretions of all the various species of Nicotiana 

 are variable in amount and in time of appearance in the development 

 of the flower and respond differently to varying climatic conditions. 

 We have found that of the F^ hybrid and the two parent species with 

 which we are concerned the amount of secretion appearing on the 

 stigmatie surface is greatest in the case of N. .sylvestris, is less in 

 F^HSS, and is still less in the case of N. Tab. var. macrophylla. The 

 amount that can be collected from any one of the three varies from 

 day to day, but is always very evidently a stigmatie secretion and not 

 a drop of condensed moisture such as can often be found in the 

 corolla tube. The secretions were collected as drops on a cover-glass 

 on the day of the experiment and from flowers whose anthers were 

 about to open. In the majority of cases these flowers were under bag. 

 A small quantity of the desired pollen was dusted into the drop of 

 stigmatie fluid, the cover-glass inverted on a hollow-ground slide and 

 the preparation sealed with a drop of distilled water. This hanging- 

 drop culture was examined after lying for five hours in a moist 

 (•h;niil)ci' at 20° C. Germiiuilidn wiicro indicated in tabic 1 means 

 the production of pollen-tubes by approximately seventy-five per cent 

 of the pollen-grains present in the culture. 



