Johnson: Sexuality in Plants 



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FERTILE AND STERILE POLLEN GRAINS 



Pollen of the first generation hybrid of the Florida Velvet bean {Stizolobinm deeringianum) 

 and the China bean (5. niveum var.). In this as in many other crosses of distinct species 

 of plants, half the pollen is sterile and half the ovules aborted. Scale in tenths and hun- 

 dredths of millimeters. Photograph by John Belling, Gainesville, Fla. (Fig. 4.) 



Millington that the stamens serve as 

 the male organs of the plant. Thus 

 Grew concludes (p. 173) that when the 

 anther opens the "globulets in the thecae 

 act as vegetable sperm which falls upon 

 the seed-case or womb and touches it 

 with prolific virtue." But this guess, 

 though it proved correct in the main 

 point, was still a guess, and not sup- 

 ported by any critical evidence so far 

 as recorded by Grew. The only ade- 

 quate evidence that could be obtained 

 on this question, while microscopes and 

 technique were still so imperfect, was 



experimental evidence. This kind of 

 proof was first given, some 20 years 

 after Grew's work, by Rudolph Jakob 

 Camerarius, of Tubingen. Camerarius 

 fully appreciated the presence of a real 

 problem here. He also had the genius 

 to see that the philosophical attempts 

 of many of his immediate predecessors, 

 to discover its solution entirely in their 

 own inner consciousnesses, were futile. 

 With the insight of a modem experi- 

 menter Camerarius put the question 

 to the plants themselves. The results 

 of his experiments, as reported in the 



