95 



Photosynthesis in Submerged Land Plants. 



By Harry V. Heimburger. 



Detiner,' in his "I'mctica! I'lanl I'h.v8i<)lo.;j;y." descriljes an experiment 

 til sliiiw the evolution of oxygen in photosynthesis. He uses lor tliis pur- 

 pose a water plant which is phiced under a glass tunnel in a vessel of 

 water and the evolved gas collected in a test tube. The same experiment 

 is described in a number of text-books, mention usually being made that 

 Wider plants must be used. Elodea, Alyriophyniim. Ccratopln/IIitin. Hiji- 

 j.nrh Pohundgcton, Vhara and Spii'ogiira are suggested by various writ- 

 ers. It is to be inferred from most of the texts that no especial ditiiculty is 

 luet in performing this experimeut, though a few of the authors consulted 

 mention some difiiculties and suggest that the experiment is uot always 

 entirely satisfactory. One writer says, "It is better to allow the apparatus 

 to stand several days in the sunlight in order to catch a full tube of the 

 gas."-' Another says. "After two or three days of hot sun, enough of the 

 gas can be obtained to make the oxygen test."" Again we are told, "The 

 glowing of the splinter shows that the gas is oxygen"^ intimating that a 

 very ])ronuunced test is not to be expected; though others say that tlie 

 spark bursts at once into flame. 



In one text'' the use of watercress in the experiuient is recommended. 

 A few of tlie texts examined, do not say definitely what sort of plants to 

 use, but usually it is implied that water plants are recjuired. In only one 

 text, of those we have been able to examine, is it even intimated that land 

 plants may be used. Doctor Coulter" says, "If an active leaf or a water 

 plant be submerged in a glass vessel, and exposed to the light. Itubbles 

 may be seen coming from the leaf surface and rising through the water." 

 The illustration accompanying this text shows what appears to be the leaf 

 of some tree or shrub. In several texts it is expressly emphasized that 

 land plants will not serve for this purpose. Atkinson says.' "Land plants. 



' Detmer-Moor. Practical Plant Physiology, pp. 35-37. 



- Atkinson, College Botany, p Gl2. 



■' Muntpf, Essentials of Biology, p. 126. 



' Atkinson, Elementary Botany, p. .51. 



^ Reynolds Green, Vegetable Physiology, p. 164. 



'■ Coulter. Plant Relations, pp. 29, 30. 



'Atkinson, Elementary Botany, p. 51. 



