128 LIFE: ITS NATURE AND ORIGIN 



An indication of how chemical control by trace substances may domi- 

 nate fertility and thereby contribute an important factor to the course 

 of evolution, is found in the Golden Rose strain of Petunia, which is 

 completely self-sterile under natural conditions. Microscopic examina- 

 tion shows that its pollen tubes grow slowly, and that even before the 

 most rapidly growing tubes reach half way down to the ovary, an 

 abscission layer forms and blocks the way. Yasuda found that the 

 placenta in the ovary of Petunia violacea secrets a "special substance" 

 which diffuses into the style and completely inhibits pollen germination 

 and tube formation. W. H. Eyster 73 found evidence that the ovarian 

 secretion of the Golden Rose Petunia "which renders the plant self- 

 sterile, can be transferred to other plants and renders them cross- 

 sterile with pollen from self-sterile plants." Golden Rose Petunia 

 can be self-fertilized by two methods: (1) "If flower buds which are 

 beginning to develop anthocyanin in the petals are opened and 

 pollenated with pollen from fully opened flowers from the same plant, 

 seed capsules containing viable seeds are produced"; similar results 

 were found by Yasuda 74 who calls this homo-pollination; (2) by spray- 

 ing the flowering plants with a solution of ten parts of a-naphthalene 

 acetamide in one million parts of water. 



"Flowers which are sprayed with this solution immediately before 

 or shortly after they have been self-pollinated produce seed capsules 

 filled with viable seeds in exactly the same way that normal self-fertile 

 plants of other strains produce seeds. Obviously a-naphthalene aceta- 

 mide neutralizes the effect of the ovarian secretion which diffuses into 

 the style and inhibits or greatly retards the growth of the pollen 

 tubes." 



Dwarfism in certain plants (e.g., maize, pea) has been shown to be due 

 either to deficiency of auxin (growth hormone) or to its destruction by 

 oxidative enzymes. J. van Overbeek 75 further found that "laziness" 

 in maize (a prostrate habit of growth) is consequent upon higher con- 

 centration of auxin in the upper part of the plant, whereas normally 

 the reverse is true. He concludes: "It is thus evident that the lazy 

 gene interferes with the auxin distribution in the stems which normally 

 takes place under the influence of gravity." 



While it has for some time been known that over about 1.5 parts 

 per million of fluorine in drinking water generally produces a dis- 

 coloration of the teeth known as "mottled enamel" (endemic dental 

 fluorosis), Dr. H. Trendley Dean and collaborators 76 have found that 

 fluoride levels of less than 1.0 ppm were accompanied by a correspond- 

 ing increase in dental caries. While the function of fluorine has not 

 yet been established, it seems possible that the liberation of fluorine 

 ions locally, by acid-producing bacteria would result in the inhibition 

 or death of the bacteria if the fluorine concentration became sufficient 



