CHEMICAL PEOCESSES IN CELLS. 141 



and is converted into affinity. This is the indispensable condition of 

 the reduction'of C0 2 and H 2 and the elaboration of organic compounds ; 

 or, in other words, " there can be no vegetation without the sun." 



The process which we have found to take place in vegetable cells 

 only holds good in the case of green plants under the influence of the 

 sunlight, for there is in all cases a double chemical process going on in 

 plant-cells. The assimilation through deoxidation of organic com- 

 pounds under the influence of sunlight has already been described. 

 This process is, however, limited to the chlorophyll plants, and in them to 

 the time when they are exposed to the sun's light and heat. Another 

 process, however, is continually going on in all forms -of vegetable cells. 

 The products of assimilation undergo within the vegetable cells various 

 chemical changes which are not accompanied by a liberation of oxygen, 

 but by a change of molecular arrangement, associated with the absorption 

 of a small amount of ox3 r gen and the setting free of carbon dioxide. 

 These changes are independent of the sunlight, and result in a diminution 

 of the mass of assimilated materials. That a plant may increase in size 

 it is necessary that the deoxidizing activity and assimilation produced in 

 the sunlight should overbalance the loss through oxidation which is 

 continually going on, whether in darkness or light. This latter process 

 in plants, by which they absorb ox3'gen and set free carbon dioxide, is 

 clearly analogous to the processes of respiration in animals. This res- 

 piration in plants is, however, very feeble, and is far overbalanced hy the 

 processes of assimilation ; therefore, as a rule, although the elaboration 

 of vegetable products is accompanied by accumulation of force, the 

 vital processes in plants which are not connected with assimilation are, 

 as in animals, dependent upon oxidation processes, and may be accom- 

 panied by the liberation of heat and electrical movement of protoplasm, 

 and the formation and growth of cells. In the case of the non-chlorophyll- 

 bearing plants, such organisms absorb organic matter already elaborated ; 

 the parasitic plants may, therefore, be regarded as a connecting-link 

 between the animal and vegetable kingdoms, especially as some of the 

 lower forms of the former are also possessed of chlorophyll, by which 

 they are enabled to decompose C0 3 under the influence of the sun. A 

 curious exception to the characteristics of the vegetable chemism is the 

 power which certain plants possess of attracting, seizing, and digesting 

 insects. The so-called insectivorous plants of Darwin and Hooker, such 

 as the Drosera rotundifolia, Darlingtonia, Nepenthes, etc., are supplied 

 with special urn-like vessels, in which the animals are trapped and 

 digested. They are lined with glands that secrete both the sugary fluid 

 to attract the insects and a true digestive juice, containing pepsin and 

 acid, which is poured out when the plants are stimulated by contact with 

 digestible substances. This secretion will turn fibrin into peptone, but 



