468 PLANT GROWTH SUBSTANCES 



to the conditions necessary for the development of immature embryos 

 and of those which fail to mature in the seed. The most successful efforts 

 in defining the growth requirements for immature embryos are those of 

 Sanders and Burkholder (51) discussed later in this paper. Unfortunately 

 their investigations do not establish the vitamin requirements of the 

 embryos, if any. From scattered observations we know a little of the 

 vitamin requirements of the embryos of higher plants. Kogl and Haagen- 

 Smit (23) found that biotin and thiamin increased the growth of pea 

 embryos freed of their cotyledons; Bonner et al. reported that panto- 

 thenic acid (9), ascorbic acid (3), or niacin (4) benefited pea embryos; 

 Noggle and Wynd (37) state that niacin induced good germination and 

 excellent development of Cattleya. 



Tumor Tissue. — Plant tumors and "accustomized" tissues in contrast 

 to normal tissues excised from stems or storage organs grow in a sugar- 

 mineral salt medium with no supplements. They do not require an 

 external supply of lAA; their growth may be improved by thiamin. 

 Judging from the evidence presented by Gautheret and his colleagues 

 (24,34), "accustomized" tissue and at least some kinds of plant tumor 

 tissues have an enhanced power to synthesize lAA.* 



An obvious explanation for the difference in growth requirements of 

 normal tissue as compared to "accustomized" tissue or tumor tissue is 

 that in becoming tumerous or in becoming "accustomized"! the original 

 tissue has mutated (14) and developed a strain with greater ability to 

 synthesize lAA. It is impossible to say whether the mutation is nuclear 

 or cytoplasmic. 



Somatic mutations (or saltations) resulting in increased power of 

 synthesis are known elsewhere in the plant kingdom and there is no 

 a priori reason why such mutations, spontaneous or induced, should not 

 occur in higher plants. We have studied a strain of Fusarium avenaceum 

 which evidenced a complete deficiency for biotin. A spontaneous mutant 

 isolated from this strain was able to synthesize its own biotin (44). Many 

 species of fungi produce spontaneous somatic mutants with enhanced 

 powers of growth. The greater vigor of mutants (pleomorphisms) of 

 some of the dermatophytes as compared to the strains from which they 



*Riker, Henry, and Duggar (38) found no more auxin in crown-gall tissue 

 than in normal tissue. 

 fSee the observations of Morel (33) . 



