VIII.J THE BEAN-PLANT. 73 



spores, and the prothallus which they develope does not 

 leave the cavity of the spore, but remains in it like an 

 endosperm. 



The physiological processes which go on in the higher 

 green plants, such as the Fern and the Bean, resemble, in the 

 gross, those which take place in Protococcus and Chara. 

 For such plants grow and flourish if their roots are im- 

 mersed in water containing a due proportion of certain 

 saline matters, while their stem and leaves are exposed 

 to the air, and receive the influence of the sun's rays. 



A Bean-plant, for instance, may be grown, if supplied 

 through its roots with a dilute watery solution of potassium 

 and calcium nitrate, potassium and iron sulphate, and mag- 

 nesium sulphate. While growing, it absorbs the solution, the 

 greater part of the water of which evaporates from the ex- 

 tensive surface of the plant. In sunshine, it rapidly decom- 

 poses carbonic anhydride, fixing the carbon, and setting free 

 the oxygen ; at night, it slowly absorbs oxygen, and gives off 

 carbonic acid ; and it manufactures a large quantity of pro- 

 tein compounds, cellulose, starch, sugar and the like, from 

 the raw materials supplied to it. 



It is further clear that, as the decomposition of carbonic 

 anhydride can take place only under the combined influences 

 of chlorophyll and sunlight, that operation must be con- 

 fined, in all ordinary plants, to the tissue immediately be- 

 neath the epidermis in the stem, and to the leaves. And 

 it can be proved, experimentally, that fresh green leaves 

 possess this power to a remarkable extent. 



On the other hand, it is clear that, when a plant is grown 

 under the conditions described, the nitrogenous and mineral 

 constituents of its food can reach the leaves only by passing 

 from the roots, where they are absorbed, through the stem 

 to the leaves. And, at whatever parts of the plant the nitro- 



