VIIL] THE BEAN-PLANT. 75 



are presented by the Conifers and the Club-mosses. For, 

 in the Conifers, the protoplasm of the embryo sac gives 

 rise to a solid prothallus-like endosperm, in which bodies 

 called corpuscula, which answer to the archegonia, are formed; 

 and in these the embryo cells arise; while, in some of the 

 Club-mosses, there are female spores distinct from the male 

 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 immersed in water containing a due proportion of 

 certain saline matters, while their stem and leaves are ex- 

 posed 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 

 extensive surface of the plant. In sunshine, it rapidly 

 decomposes carbonic anhydride, fixing the carbon, and 

 setting free the oxygen ; at night, it slowly absorbs oxygen, 

 and gives off carbonic acid j and it manufactures a large 

 quantity of protein 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 in- 

 fluences of chlorophyll and sunlight, that operation must 

 be confined, in all ordinary plants, to the tissue imme- 

 diately beneath the epidermis in the stem, and to the 



