66 PLANT GROWTH SUBSTANCES 



a slip In technique and not to the cross intended. In 5 cases sectioned 

 material showed that fertiUzation had occurred but growth had not 

 proceeded far enough to be detected with a dissecting microscope. There 

 were 21 cases which have been recorded as negative, presumably because 

 the pollen tubes were not able to reach the ovary. 



Embryo culture of hybrids of our 10 species of Datura raises many 

 problems. It has taught us to think of growth and development as 

 determined by the internal microenvironment through the interaction 

 and balance of chemical stimulators and inhibitors. Even now with our 

 limited knowledge and inadequate techniques the possibilities of greatly 

 increasing the number of wide species' hybrids, some of which may 

 be transformed into pure-breeding new species, is certainly alluring. 

 With further knowledge and improved techniques more of the barriers 

 to crossability may be found to be removable, and plant breeders may 

 inaugurate an age of massive miscegenation. It may then be possible 

 to answer the question of our introduction and to say that we can cross 

 corn and beans. It will be interesting to see what the offspring will 

 be from all these crossings. 



In closing I wish again to apologize for speaking only of work on 

 Datura. Other investigators might make similar statements about the 

 plants with which they have been working. With examples from studies 

 of the plant which I know best I have tried to emphasize the desirability 

 of learning all we can regarding the intimate structure and behavior of 

 the ultimate elements of the plant, but also of interrelating this knowl- 

 edge toward a better understanding of the whole life of the plant and 

 especially toward the utilization of this knowledge in the conscious 

 control of its life processes and evolution. 



Knowledge is indeed power — potential power — but knowledge which 

 is not put to work is sterile. 



