4 8 



THE SYNTHESIS OF CARBOHYDRATES 



a complete culture medium whether light or temperature be 

 limiting. This is shown in the accompanying table of some of 

 Briggs's results which gives the real assimilation per 50 sq. 

 cm. of surface expressed in percentages of the rate observed in 

 plants growing in the normal culture solution or in pot culture 

 when light and temperature were limiting. 



It will be seen that photosynthesis is subnormal when light and 

 temperature are limiting, which means that subnormality in 

 the photochemical phase, which is more influenced by illu- 

 mination, is accompanied by a subnormality in the chemical 

 phase which is mostly influenced by temperature ; further, 

 both phases generally show the same degree of subnormality. 

 In passing it may be observed that the particular form in 

 which an element is presented to the plant may be of impor- 

 tance. This is shown by the following table taken from Mas- 

 kell's observations on starch production in the leaves of the 

 potato,* from which he concluded that the amount of starch 

 varies not only with the ordinary conditioning factors but 

 also with the nature of the available potash. Thus potassium 

 sulphate when added to the soil was found to be more effective 

 in starch production than treatment with potassium chloride 

 and other potassic manures. The figures given are the mean 

 values of colorimetric estimations made over a period of 



Treatment. 

 No potash (control) 

 Potassium sulphate 

 Potassium chloride 

 " Potash manure salts 



Starch Production. 

 2-OI3 

 2-667 

 2-139 

 1-893 



seventeen days in September ; the quantities of added mineral 

 manure were so controlled that the culture plots were given an 



* Maskell : "Ann. Bot." 1927, 41, 327. 



