DIGESTION OF RESERVE-MATERIALS 229 



The same form of diastase is found in all parts of sproutmg 

 potato tubers, but is especially abundant near the ' eyes ' where 

 growth commences. It converts the starch of the tuber into 

 sugar, which latter compound is subsequently transported to 

 the growing shoots. Small amounts are also secreted by the 

 ' aleuron-layer ' in the endosperm of cereal grains when germina- 

 tion takes place. Translocation-diastase acts more readily at 

 lower temperatures than the diastase of secretion and dissolves 

 starch-grains without previously corroding them. 



{b) During the germination of the cereal grains it is found that 

 the cell-walls of the endosperm-tissue lying near the embryo 

 and near the ' aleuron-layer ' are disintegrated and dissolved by 

 the activity of an enzyme, which commences its work before the 

 diastatic enzyme begins to dissolve the starch in the grain. 



This enzyme, named cytase, is secreted partially by the 

 epithelium of the scutellum, but more especially by the cells 

 of the ' aleuron-layer.' It is also present in the cotyledons of 

 germinating peas and in the endosperm of buck-wheat. Its 

 function in these cases appears to be that of getting rid of the 

 cell-walls, so as to allow of an easier diffusion and therefore a 

 more rapid action of diastase upon the starch-reserve. 



Cytase is also found in the seeds of the date-palm, and is most 

 probably present in germinating seeds of all those plants whose 

 store of reserve-food for the embryo consists of thickened 

 cell-walls composed of hemicelMose. 



(ii) The reserve-material, inuUn, which is present in the tubers 

 of the Jerusalem artichoke, is transformed when germination 

 begins into levulose by the action of an enzyme named inulase. 

 The existence of the same enzyme has been demonstrated in 

 the growing bulbs of snowdrop and other liliaceous plants 

 which contain inulin. 



(iii) A very common reserve-material of wide distribution 

 in the vegetable kingdom is cane-sugar. Experiments suggest 

 that as such it is of little or no value for the immediate 



