3-1: PLANT STUDIES 



of oxygen and the giving out of carbon dioxide. It will be 

 noted at once that this is exactly the reverse of wlnit takes 

 place in jihotosynthesis. During the day, therefore, carbon 

 dioxide and oxygen are both Ijeing al)sorbed and evolved. 

 It will also be noted that the taking in of oxygen and the 

 giving out of carljon dioxide is just the sort of exchange 

 which takes place in our own respiration. In fact this pro- 

 cess is also called respiration in plants. It does not depend 

 upon light, for it goes on in the dark. It does not dejoend 

 upon chlorophyll, for it goes on in plants and parts of plants 

 which are not green. It is not 23eculiar to leaves, but goes 

 on in every living part of the plant. A process which goes 

 on without interruption in all living plants and animals 

 must Ije very closely related to their living. We conclude, 

 therefore, that while photosynthesis is peculiar to green 

 plants, and only takes place in them when light is present, 

 respiration is necessary to all plants in all conditions, and 

 that when it ceases life must soon cease. The fact is, 

 respiratioji supplies the energy which enaljles the living 

 substance to work. 



0)ice it was thought that plants differ from animals 

 in the fact that plants absorb carbon dioxide and give off 

 oxygen, while animals absorl) oxygen and give off carljon 

 dioxide. It is seen now that there is no such difference, 

 but tlnit resi)iration (absorption of oxygon and evolution of 

 carbon dioxide) is common to both plants and aninnils. 

 The difference is that greei\ plants have the added work of 

 j)hotosynthesis. 



We may also call the foliage leaf, therefore, nn iirijan of 

 respiration, l)ecausc so mudi of s'.ich W(n'k is done bv it, 

 but it must lie rememltered that respiration is o-oino- o^ in 

 every living part of the plant. 



This by no means com]iletes tlic list of functions that 

 might bi^ iiia,de out for fo]ia,ge leaves, but it serves to 

 indicate both their peculiar work (i)hotosvnthesis) and 

 the fact that they are doing other kinds of work as well. 



