,n BOTANY 01 THE LIVING PLANT 



musl be supplied in particular forms 



i iably utilised by the plant. Thus sulphur 



and phosphorus must be in the form of sulphate and phosphate 



trvely, while nitrogen is mosl suitable in the form of nitrate, 



<>r of unmonium Baits. 



Though the reasons why the elements mentioned should be essen- 

 tial to plant lopment scarcely fall to be considered at this point, 

 it may be mentioned thai nitrogen, sulphur and phosphorus are 

 requir protein syntl while magnesium is a constituent of 

 olorophyU molecule. The absence of iron also interferes with 

 chlorophyll formation and leads to a condition of chlorosis, in which 

 the l< have a sickly yellow colour. The reason of this may 

 that iron acts as a catalyst in the building up of the complex 

 molecule of chlorophyll. Iron and its compounds may also serve as 

 in the cell in other connections, while the same applies 

 to potassium. Calcium is essential since it is a constituent of the 

 pectic bodies which, as mentioned on p. 24, enter into the composition 

 of the cell -wall, particularly of the middle lamella. The application 

 within the plant of elements such as boron is at present uncertain. 

 In addition to these uses of elements derived from the soil, it is certain 

 that inorganic salts and ions figure in the actual make-up of proto- 

 plasm (Chapter III), and in regulating its activity. 



The Soil and Plant Distribution. 



The essential materials required from the soil are much the same 

 for all plants. It is, however, a matter of common observation in the 

 1 and in the garden that a soil which favours certain plant species 

 1- unfavourable to others. Some plants require more of a particular 

 rial than do oth. This applies especially to water, and 



the water-content of the soil, which depends on the climate, on 

 make-up of the soil and on topographical conditions, is a very 

 important factor in plant distribution. Requirements also vary with 

 I to mineral nutrients. Thus some plants, such as the Nettle 

 ^ rtlca til " 1 to have a high nitrogen requirement and 



Irish best in the vicinity of dwellings or in other positions where 

 n and nitrates are relatively abundant. Among culti- 

 thep high potassium, and swedes and turnips a 



hphosphoru uirement. The distribution of plants is markedly 

 the P r< »n tlu-M.il of lime or other compounds of cal- 



cium. Some plan* - heep's Sorrel (Rumex acelosella), Heather 



