64 THE LIFE OF THE PLANT 



them a pressure equal to that of several atmospheres. 

 Anatomists make use of this property of seeds when 

 they wish to separate the bones of the skull : the 

 cavity of the skull is usually filled with beans, which are 

 then moistened. The bones of the skull separate at 

 the sutures owing to the strong and uniform pressure 

 all over the inner surface of the skull. 



Such is the mechanical effect of water upon seeds ; 

 it enables them to shed their coats which they no longer 

 need, and to overcome the resistance of the surrounding 

 particles of soil. But the chemical action of water is still 

 more important : without it the solution and consequently 

 the transfer of the stores of nutrient substances cannot 

 take place. Water, however, is not alone sufficient for 

 the purpose, because all these substances, as we have 

 seen, are insoluble in water ; in order to become available 

 for nutrition they must first of all be changed into other 

 substances. Starch, for instance, could be dissolved 

 in water if previously changed into the sugar, glucose. 

 Such a transformation is possible — the preparation of 

 starch sugar is based upon it, and it can easily be proved 

 that such a transformation actually takes place. We have 

 only to taste a raw barley grain and then a malted grain, 

 i.e. a germinating barley grain, to realise that the former 

 is tasteless whereas the latter is sweet. But perhaps the 

 taste has deceived us ; in that case we can avail ourselves 

 of a test I described in our last lecture. We have seen 

 how the blue liquid — Fehling's solution — gives with 

 glucose a bright red precipitate. We take malt mixed 

 with water, add to it Fehling's solution, and get a red 

 precipitate. We cut off a thin slice of a germinating 

 seed, place it under the microscope, add a drop of the 

 same Fehling's solution, and get a red colouration in the 

 cells. Therefore the taste as well as the more con- 

 clusive chemical reaction prove that sugar appears in 

 the germinating seed. But is it true that this sugar is 

 formed from starch ? Both quantitative analysis and 



