95 



Photosynthesis in Submerged Land Plants. 



By Harky V. Heimbukger. 



Detnier.' in his "I'mctica! I'laiii I'hysiulo^y." desoribe.s an experiment 

 to show the evolution of oxygen in photosynthesis. He uses for this pur- 

 po.se a water plant whieli is placed under a glass funnel 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 

 writer plants smist be used. Elodca, MyrioplniUHni, Ccratdiiln/lliiiii. flij;- 

 liiirh J'()l(iiii<i(j<toii. Cliiini and ^pirof/i/i'u are suggested by various writ- 

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

 met in performing this ex])eriment, though a few of the authors consulted 

 mention so]ne difficulties and suggest that the experiment is not always 

 entirely satisfactory. One writer says, "Tt 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 iironounced test is not to be expected: thongh others say that the 

 spark bui'sts at once into flame. 



In one text^ the use of watercress in the experin^ent is reconnnended. 

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

 use, but usually it is implied that water plants are required. 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, bubbles 

 ma.y be seen comiug from the leaf surface and rising through the ^^ater." 

 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 tliis purpose. Atkinson says," "Land plants. 



^ Detmcr-Moor, I'rrtctical Plfint Physiol ogy, pp 35-37. 



- Atknison, Collego Botany, p G2. 



•' Iliintpi-, Essontials or" 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. 



