ASSIMILATION OF CARBON 



37 



An adequate supply of water in the leaves is essential to the normal progress 

 of photosynthesis; according to Sachs and Nagamatsz 1 no starch is formed 

 by wilting leaves, a fact which Stahl believed to be due to the stomatal 

 closure that accompanies wilting. This interpretation is supported by the obser- 

 vation that leaves in which the stomata remain open even in the wilted condition 

 (Rumex aquaticus, Caltha palustris, Hydrangea hortensis, Calla palustris) still 

 continue to accumulate starch after wilting has occurred. 



Finally, an excess of salts in the soil has a retarding effect upon the rate of 

 carbon dioxide decomposition. Schimper found that watering with sodium 

 chloride solution caused development to cease in most plants 

 (non-halophy tes) , through a checking of photosynthesis. Ac- 

 cording to Stahl this, also, is due to stomatal closure, caused 

 by excess of salts. If the leaves are slightly wounded so 

 as to facilitate entrance of carbon dioxide into the tissue, 

 starch accumulates about the wound margins. True halo- 

 phytes grow, though slowly, upon soils rich in salts, since 

 their stomata do not close at all. 



§9. Nutrition of Green Plants by Organic Compounds. 

 Green plants can also use as food organic compounds that 

 are supplied from without. 2 This form of nutrition may 

 go on simultaneously with the assimilation of carbon 

 dioxide from the air, which is especially true in the case of 

 insectivorous plants. 3 These latter are green and can 

 assimilate carbon dioxide, but, at the same time, they are 

 provided with a characteristic mechanism for catching and 

 digesting insects (Fig. iq). In this class, for instance, / e IG un ^ e P ^Vt1on 

 belongs the widely distributed sundew (Dr sera rotund if olio) , of which was covered 

 which grows in bogs. Its leaves are covered with pin 

 shaped tentacles or glands, which secrete a sticky fluid 

 As an insect alights upon the leaf, the tentacles bend toward j£j?J reaction with 

 it, a copious flow of an acid liquid containing a pepsin-like 

 enzyme takes place, and the insect is digested. Sundew can also digest and 

 absorb lean meat and white of egg. In Nepenthes 4 a part of the petiole 

 is modified into a tankard-shaped structure with the leaf-blade acting as a 

 cover. The hollow portion contains a weakly acid solution, in which 

 imprisoned insects are digested. Each leaf of Dionaea muscipida consists 

 of a flattened petiole and a round leaf-blade divided by the midrib into 

 halves, like the halves of an open mussel, separated by an angle of from 60 to 

 90 degrees. The free margin of each lobe is extended into sharp, slender teeth, 

 and each lobe bears on its upper surface near the center three very elastic 



1 Nagamatsz, Atsusuke, Beitrage zur Kenntnis der Chlorophyllfunktion. Arbeit. Bot. Inst. Wiirzburg 

 3:389-407. 1888. 



2 Apparently carbon monoxide cannot be assimilated; see: Krascheninnikoff, Th., La plante verte 

 assimile-t-elle l'oxyde de carbone? Rev. gen. bot. 21 : 177-193. 1909. 



3 Darwin, Charles R., Insectivorous Plants. London, 1875. 



4 Clautriau, G., La digestion dans les urnes de Nepenthes. Recueil Inst. Bot. Bruxelles 5: 89-133. 

 1902. Vines, S. H., The proteolytic enzyme of Nepenthes (III). Ann. bot. 15 : 563-573. 1901. 



with cocoa butter dur- 

 ing exposure to light. 

 This portion shows no 



