362 



PLANT GROWTH SUBSTANCES 



the transformation of other types of precursors (3,2). The existence of 

 such precursors in the unfertiHzed ovary tissue of Nicotiana tabacum 

 and Antirrhinum is indicated by the yields of auxin obtained following 

 hydrolysis with o.i N HCl as shown in Table 4. Hydrolysis of Nicotiana 

 tissue with i .0 N NaOH gives equal yields of auxin, but similar hydrolysis 

 of Antirrhinum tissue does not. 



Hatcher (7) proposes that for rye the auxin system of the anther is 

 different from that of the pistil, since in the former the maximum amount 

 of auxin is found 2 to 3 weeks earlier than in the pistil and later disappears 

 completely while the auxin of the mature pistil can be recovered by 



TABLE 4 

 Auxin yields from 20 mg. ovary tissue following hydrolysis 



alkaline hydrolysis. He infers that auxin-a is the principal auxin of the 

 embryo and indoleacetic acid is the principal auxin of the endosperm, 

 the latter being the auxin concerned in the development of the pistil 

 and anther. However, Zimmerman and Hitchcock (22) have found that 

 negative results for indoles are obtained when active extracts of corn 

 pollen are tested by the Winkler method, and they suggest that auxin-a 

 may be the principal auxin of such extracts. A comparison of the yields 

 of auxin from pollen and ovary tissue by hydrolysis with i.o N NaOH 

 or 0.1 N HCl strongly suggests the existence of several types of auxin 

 (Tables 4 and 5). The auxin of the pollen of Nicotiana and Datura 

 is alkali-stable, acid-labile, and therefore indicated to be indoleacetic 

 acid whereas the pollen of Antirrhinum contains indoleacetic acid and an 

 acid-stable auxin or auxin-a. Similarly in the ovary tissue of Nicotiana 

 and Antirrhinum there appears to be both acid-stable and alkaU-stable 

 auxins. These are tentative interpretations, however, for as Bonner and 



