94 



BOTANY OF THE LIVING PLANT 



fruiting. But the experiment m;iy l:)e varied by tlie omission of any 

 one of those elements. Any constant cliangc in the condition of the 



plant following that omission may be 

 held as evidence of the part that 

 substance plays in its normal physio- 

 logy. This is most readily exemplified 

 in the case of Iron. If the solution 

 be made up with chemically pure 

 materials, the result of growing it 

 without Iron is that after the first 

 leaves, which may appear pale green, 

 the later leaves develop yellowish. If 

 carried far the subject of the experi- 

 ment will appear starved. If after 

 this pale yellov/ish, or chlorotic state 

 is well established a trace of Iron Salt 

 be added to the solution, the normal 

 green colour will be developed, appear- 

 ing first along the veins ; or even if it 

 be applied locally to the surface of the 

 leaves, the full green colour will appear 

 at those points where the Iron Salt has 

 been applied. The conclusion is that 

 Iron is essential for the formation of 

 the green colour, and that a very 

 small quantity of it suffices. Similar 

 experiments may be made bv omit- 

 ting other elements from the recipe, 

 p,(, -g^ for instance Potassium (Fig. 70): Such 



Water-culture of Buckwheat. I. shows rCSldtS SCrVC tO show hoW important 

 a culture where a full nutrient solution , ^t^ ■ ■ r- ■ ■ 



was supplied. II. shows the result of the Transpiratioii-Strcam IS m supplv- 



the omission of potassium. (From Stras- . i r i -i 



burger, after Nobbe.) lUg thc ucccssary Salts ironi the soil. 



Water-Economy. 



Thc maintenance of the Transpiration-Stream is also important for 

 the preservation of mechanical rigiditv in thc succulent parts. The 

 flaccid and limp condition of the withering shoot, and the recovery 

 which it shows on sufficient w<iter-supplv, arc matters of common 

 knowledge. Both arc referable to the turgor of thc mdix-idual cells, 

 whieji falls when water is delicient, and thc firmness nf the whole tissue 



