THE B VITAMIN REQUIREMENTS OF ANIMALS AND PLANTS 317 



isoleucine, valine, glutamic acid, proline, and serine. 47 - 48 Thiamine is 

 apparently not synthesized by any roots, 49 but is necessary for their 

 growth, and is active in dilutions as low as 1 :4x 10 13 . 50 There is also some 

 evidence to indicate that it is a stimulating factor for root formation. 51 

 Roots are apparently able to utilize the thiazole and pyrimidine fractions 

 of thiamine about as well as thiamine itself. 52 Some, such as the tomato 

 root, require only the thiazole portion, being able to synthesize the 

 pyrimidine part; but others, such as the pea root, can synthesize neither 

 part, requiring a nutritional source of both. 



Work with plant embryos requires that the embryo be removed from 

 the seed and the cotyledons from the embryo as early as possible. When 

 these precautions are taken, the resulting embryo is found to be a 

 heterotrophic organism, requiring a nutritional source of at least some 

 of the B vitamins. Thiamine and nicotinic acid have been found to be 

 required by most roots and embryos, while pyridoxine is required by a 

 lesser number. The requirement for riboflavin and pantothenic acid is 

 less clearly known, due to less thorough study. The requirements for the 

 more recently discovered members of the B group of vitamins have not 

 been reported to date. A summary of much of the known data is shown 

 in Table 19. 



Table 19. Known B Vitamin Requirements of the Roots and Embryos of Some Green Plants 



+ = require (for thiamine, require both parts of molecule). 

 S = stimulates growth. 

 — = not required. 



1 = thiamine and niacin alone as effective as yeast extract. 



2 = requires thiazole portion of thiamine only. 



In summary, we find that the ability of green plants to synthesize B 

 vitamins is very unevenly distributed, and is concentrated generally in 

 those parts of the plant reserved specifically for general synthetic activity. 

 To what extent the activities of the various tissues of animals vary in 

 respect to B vitamin synthesis is largely unknown. While green plants as 

 a whole survive readily without an exogenous source of B vitamins, it 

 seems apparent that parts of the plant (and phases in its life) exist that 



