214 PLANT PHYSIOLOGY 



is insured. It is interesting to note that of all the vitamins, this 

 and vitamin G are the only ones found in plants lacking chloro- 

 phyll. Yeast is one of the best sources of this vitamin and is the one 

 generally used to cause recovery from experimental B-avitaminosis. 

 Vitamin B can apparently be synthesized by yeast as well as by 

 other microorganisms, including various molds and bacteria (Sun- 

 derland and Werkman, 1928) . 



Bios. — In 1901 Wildiers noticed that yeast did not grow well 

 on a purely synthetic medium, and explained this by assuming that 

 the yeast required some unknown substance, to which he gave the 

 name of bios. He believed that the yeast could not produce its 

 own bios but must get it from external sources. The word "bios" 

 has since been reserved for growth-promoting factors for yeast, 

 but the term is still very much confused and is used by different 

 workers to mean (a) a growth stimulant, (b) an essential factor 

 for growth, and (c) a factor stimulating the production of carbon 

 dioxide. Some kinds of yeast seem to require it for growth, while 

 for others it acts only as a stimulant. 



Also much has been written to prove and to disprove that bios 

 is the same as vitamin B. The evidence against the identity of 

 these two substances is now overwhelming, but they are, never- 

 theless, distinctly related. While some yeasts will grow without 

 bios in the medium, they do not have any antineuritic potency, 

 which has led Funk and others to the conclusion that the yeast 

 requires bios for the synthesis of vitamin B. This would indicate 

 that perhaps bios is a sort of provitamin. The word "nutrilite" 

 has been proposed by Williams (1928) to include such vitaminlike 

 substances. 



Vitamin C. — Vitamin C is also water soluble and is found in 

 fresh vegetables, milk, and fruits, especially in citrus fruits and 

 tomatoes. It is very unstable and seems to be more sensitive to 

 heat than the other vitamins, although cooking will not entirely 

 destroy any of the vitamins if they are kept in a closed vessel 

 when heating, which implies that the chief injury is through oxi- 

 dation rather than direct destruction by heat. Children, however, 

 who are fed on pasteurized milk, should be given a supplementary 

 diet of fruit juices. 



Vitamin C is called the antiscorbutic vitamin since its absence 

 results in the disease known as scurvy. Formerly sailors and 

 explorers who were deprived of fresh fruit and milk were especially 



