232 PHYSIOLOGY OF NUTRITION 



which depends upon the amount of protoplasm present. As has been noted 

 (page 160), not all proteins are to be regarded as constituents of the living pro- 

 toplasm; the plant cell contains larger or smaller amounts of non-protoplasmic 

 proteins, and the question arises whether the respiration rate is a function of the 

 total protein content or of the protoplasmic proteins only. During germination 

 in darkness the total protein content is lowered while the rate of carbon dioxide 

 production gradually rises (see pages 183, 230), so that seedlings with little 

 protein, in the later stages of germination, respire more vigorously than do seed- 

 lings with more protein, in earlier stages. During this process of germination in 

 darkness, however, it is only the non-protoplasmic or reserve proteins that de- 

 crease; the proteins that are indigestible in gastric juice, which are just the 

 ones that are to be considered as part of the protoplasm, increase during germ- 

 ination (see Fig. 88, p. 184). Palladin 1 carried out parallel series of deter- 

 minations of the amounts of carbon dioxide given off by, and of indigestible 

 proteins* present in, wheat seedlings during germination in darkness. These 

 determinations showed that, in the intermediate stages of germination, with 

 adequate supply of carbohydrates, the rate of elimination of carbon dioxide is 

 proportional to the amount of indigestible protein present in the plantlet. 2 

 In later stages of germination, as has been said, the respiration rate decreases, 

 on account of the diminishing supply of carbohydrates, but the indigestible 

 proteins still continue to increase in amount. 



With the same temperature and with adequate carbohydrate supply, equal 

 amounts of carbon dioxide are produced per unit of time, for a given amount of 

 indigestible proteins. In the case of wheat germinating at a temperature of 

 from 20 to 2i°C, the ratio of the hourly rate of carbon dioxide production to the 



amount of nitrogen in the indigestible proteins of the seedling (~^J na d the 



following values, at successive stages of germination; seedlings four days old, 

 1.06; six days old, 10.5; seven days old, 1.18; nine days old, 1.15. It thus ap- 

 pears that, with a plentiful supply of carbohydrates, the respiratory rate depends 

 upon the amount of nuclein materials (taken to be proportional to the amount of 

 proteins indigestible in gastric juice) that are present in the seedling. 



This conclusion is also supported by the observation of Burlakov, 3 that em- 

 bryos respire much more actively in proportion to their weight than do entire 

 seeds. One hundred grams of wheat seeds, after soaking in water forty-eight 

 hours, gave off carbon dioxide at the rate of 15.2 mg. per hour, at a temperature 

 of from 20 to 2 2°C. The same weight of separate embryos, after soaking 

 twenty-four hours, produced 241.8 mg. per hour. The respiration of the em- 



1 Palladin, 1896. [See note 6, p. 183.] 



2 Although the amount of living protoplasm in the plant may thus be approximated in terms of the 

 amount of indigestible protein, the method is confessedly not precise, as more recent studies show. It was 

 the best available for these experiments, however. 



3 Burlakov, G. G., Sur la question de la respiration du germe de froment. [Russian.] Trav. Soc. Imp. 

 Nat. Univ. Kharkov 31 : V-XV. 1897. [Pagination in Roman numerals.] 



1 The term indigestible, as used in the text, refers to those proteins that are found to be 

 undigested by gastric juice. — Ed. 



