PHYSIOLOGY 239 



the margin, or guided by the downwardly -directed hairs, insects and other small 

 animals finally fall into the fluid and are there digested by the action of 

 ferments and acids. The larvae which CLAUTRIAU found living in Nepenthes 

 pitchers may, like intestinal parasites, be enabled to live under the conditions by 

 secreting a protective anti-ferment. In Sarrcfcenia and Cephalotus, GOEBEL was 

 unable to discover any digestive ferments ; but in Cephalotus it was possible to 

 determine that the secretions have antiseptic properties. The lid-like appendage 

 at the opening of the pitcher of Nepenthes, Sarracenia, and Cephalotus does not 

 shut ; its function seems to be merely to prevent foreign substances from 

 ('ailing into the pitcher, and particularly to keep out the rain. The entrance to 

 the tubular leaves of Durlinylonia is under the helmet-like extremity, and there- 

 fore a lid is unnecessary ( x ). 



III. Respiration 



It is a matter of common knowledge that animals are unable to 

 exist without breathing. In the higher animals the process of respira- 

 tion is so evident as not easily to escape notice, but the fact that 

 plants breathe is not at once so apparent. Just as the method of the 

 nutrition of green plants was only discovered by experiment, so it 

 also required carefully conducted experimental investigation to demon- 

 strate that PLANTS ALSO MUST BREATHE IN ORDER TO LIVE ; that, like 

 animals, they take up oxygen and- give off carbonic acid. Although 

 the question had already been thoroughly investigated by SAUSSURE 

 in 1822, and by DuTROCHET in 1837, and its essential features 

 correctly interpreted, LIEBIG pronounced the belief in the respiration 

 of plants to be opposed to all facts, on the" ground that it was 

 positively proved that plants on the contrary decomposed carbonic 

 acid and gave off the oxygen. He asserted that it was an absurdity 

 to suppose that both processes were carried on at the same time; and 

 yet that is what occurs. 



ASSIMILATION AND RESPIRATION ARE TWO DISTINCT VITAL PRO- 

 CESSES CARRIED ON INDEPENDENTLY BY PLANTS. WHILE IN THE 

 PROCESS OF ASSIMILATION GREEN PLANTS ALONE, AND ONLY IN THE 

 LIGHT, DECOMPOSE CARBONIC ACID AND GIVE OFF OXYGEN, ALL PLANT 

 ORGANS WITHOUT EXCEPTION BOTH BY DAY AND BY NIGHT TAKE UP 



OXYGEN AND GIVE OFF CARBONIC ACID. Organic substance, obtained 

 by assimilation, is in turn lost by respiration. A seedling grown in 

 the dark so that assimilation is impossible, loses by respiration a con- 

 siderable part of its organic substance, and its dry weight is consider- 

 ably diminished. It has been found that during the germination of 

 a grain of Indian Corn, a full half of the organic reserve material is 

 consumed in three weeks. That green plants growing in the light 

 accumulate a considerable surplus of organic substance is due to the 

 fact that the daily production of material by the assimilatory activity 

 of the green portions is greater than the constant loss which is caused 



