PHYSIOLOGY CHAP. 



Many monocotyledons normally exhibit no formation of starch, 

 but produce sugar in solution ; it is only when this is in excess 

 that starch in the solid form is manufactured. 



The other organic matters, fats and proteins, are formed by 

 gradual chemical change from the carbohydrates, starch and sugar. 

 The formation of oil from starch may be directly observed in the 

 seeds of certain plants. Paeony seeds, for instance, so long as 

 they are immature, contain only carbohydrates and scarcely any 

 fat. When placed in moist air, it is found after a time that all 

 the starch has disappeared by conversion into oil. In many of 

 the lower plants, e.g. Algae, the first visible product in the cell is 

 not starch but oil. 



Far more complex is the synthesis of proteins and nucleo- 

 proteins effected by the roots from the carbohydrates and derivatives 



of the nitrates, sulphates, and phosphates 

 of the soil. We know nothing about this 

 marvellous synthesis, indispensable as it 

 is to the nutrition and development of 

 II living protoplasm. It is only known that 

 oxalic acid (C.,H 2 4 ) is frequently formed 

 as a secondary product, which, in itself 

 toxic, combines, as it is formed, with lime 

 FIG. ID ceiis or Beer Yeast into an insoluble innocuous salt that 

 g? : collects in the form of a crystalline 

 powder round those parts of the plant in 

 which the formation of proteins and nucleius takes place. It 

 also seems probable that asparagine (C 4 H 8 N 2 3 ), a soluble and 

 diffusible ammo -body, is an intermediate product in protein 

 synthesis. 



From the green plants one must, in virtue of their metabolism, 

 distinguish all those plants which are lacking in chlorophyll, and 

 live as saprophytes, or parasites, or again as parasites and sapro- 

 phytes according to circumstances. The innumerable host of 

 fungi and bacteria come under this category. They have the 

 singular property of consuming in their nutrition and reproduction 

 only the minimal part of the organic matters which form their 

 food, and of destroying all the rest by processes of fermentation 

 and putrefaction, effected by enzymes contained within the cell or 

 secreted from without. 



A classical example of this mode of metabolism is afforded 

 by Saccharomyces cerevisiae (Fig. 16), which produces alcoholic 

 fermentation of glucose according to the equation : 



C f) H 12 O c =2CO 2 +2C 2 H 6 O. 



When a certain quantity of yeast is introduced into grape 

 juice, there is formed along with the development of carbonic acid 

 and the production of alcohol a small amount of glycerin, of 



