34 THEORIES ON THE ABSORPTION OF NITROGEN 



Among higher plants there are very divergent types of 

 leaf structure. In some a thin epidermis separates the cells 

 from the surrounding air; in others there is a fibrous in- 

 vestment and the cells are very crowded. It is extremely 

 probable that these differences have an enormous influence 

 on the power of absorbing nitrogen. 



Among all members of the family of the Leguminosaj 

 the leaves are large and soft. Their cells are pierced by 

 apertures or stomata which are thought to serve merely for 

 transpiration. But why should n(jt these cells be able to 

 absorb atmospheric nitrogen as well as carbonic acid ? 

 Agriculturists know that a leguminous plant, and the turnip 

 also, need only a very small initial quantity of nitrogen 

 as compared with that yielded by the crop. The author 

 aims at drawing an analogy between the large leaves of 

 the turnip, with their thin epidermis, and those of the 

 Leguminosse, which, according to him, are all large and soft. 



Cereals, on the other hand, which do not possess this 

 faculty of fixing atmospheric nitrogen to the same degree 

 as the Leguminosffi, are very sensitive to an addition of 

 nitrogenous manure, and their yield is thereby increased. 

 This is easily explained if a leaf of a cereal or of a pasture 

 grass be examined; the tissues are crowded, have but little 

 access to the air, and, further, are covered by a fibrous 

 layer. 



After a series of analyses and various experiments, the 

 author carried out numerous researches on the microscopic 

 structure of plant leaves, from which he came to the follow- 

 ing conclusions : — • 



(i) All plants, at a particular period of their growth, 

 give rise to certain specialized hairs, which produce albumen. 

 (He revealed this albumen by means of three reagents : 

 iodine, sulphates of copper and potassium, nitrate of mer- 

 cury, &c.) 



(2) All these specialized hairs are stuffed at their upper 

 ends with albumen, which, after a certain time, they allow 



