1902] CHANGE OF FORM 



103 



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bers as is given off from the external surface, and the combined 

 surfaces of the former are often greater than the latter. As 

 these air cavities are continuous through the leaf and stem up 

 into the growing parts, it follows from the laws of diffusion 

 that these latter when- illuminated must be supplied with an 

 atmosphere rich in oxygen. This internal atmosphere will vary 

 under different conditions, for during the night, or at times when 

 photosynthesis is not active, the excess of Og will diffuse out 

 and CO^ will accumulate. The gas obtained from stems of Pros- 

 erpiuaca pahistris growing in deep water and after several days 

 of dull weather contained O^ 4.4 per cent., N 35.6 per cent., CO3 

 10 per cent.; and the gas removed from the stems of Nuphar 



> during bright sunshine consisted of O^ 35 per cent., N 65 per 



cent., COg 0.6 per cent. 



> " In the case of CO^, the slowness of diffusion may counteract 



the higher percentage in the water. In a perfectly saturated 

 atmosphere, however, where the supply of CO^ and O is normal, 

 the plant for a long time continues the development of what is 

 essentially the water form. When grown in sugar (lactose) 

 solution the water form is still produced, though in these exper- 

 iments it has not yet been determined just how much growth 

 has occurred before fermentation has destroyed all the sugar. 

 It is quite possible too that the plant is unable to use the sugar 



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as food. 



Plants were grown under water in glass vessels containing 

 atmospheres of different O^ and COg pressures as follows: (l) 

 one volume of water to an atmosphere containing an equal 

 volume each of CO^ and O^ ; (2) one volume water to an 

 atmosphere of three equal volumes of CO3 and one volume of 

 ^^r; (3) one part by volume of water to three parts by volume 

 of O3 and one third part CO^. For the last experiment the CO3 

 pressure was about five hundred times and the O^ approximately 

 five times as great as that of ordinary atmosphere; while in the 



second case the O^ pressure was diminished one-third and the 

 COg pressure increased 250,000 times. In all cases the pressure 

 of the mixture was approximately 760™°" mercury; and the 



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