THE LEAF 



125 



leguinin, wliich occurs iu the seeds of legniiiinous plants. The 

 aleuron layer of cereals contains gluten-casein and gluten- 

 fibrin. The products of decomposition, too, of the albumens 

 are as different as are their degrees of solubility. Thus gluten 

 fibrin, when boiled with sulphuric acid, yields very little 

 asparagin (a substance of great importance for the transit 

 and formation of new albumens), while the other groups 

 yield a large amount. Other products of decomposition are 



FIG. 18.— A Section through the Outer Layers of a Potato Tuber. 



k, cork ; pi, cells of cortex containing protoplasm and small starch grains ; cr, tabloid 

 protein crystals ; s, starch grains (after Tschirch). 



leucin, tyrosin, glutamin, ammonia, and volatile oils. These 

 latter cause the unpleasant odour of decomposing albumens. 

 The albumens may also occur in a crystalline form in the cell 

 sap ; they are then distinguished from the inorganic crystals as 

 protein crystals. Such crystals occur in beautiful cubical form 

 in the end cells of tbe gland hairs of the potato shoots. 



The protein crystals are perhaps most easily seen in sections 

 of a potato tuber, where they occur in the cortical tissues, 



