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igo2] 



CHAXGE OF FORM IN PROSERPINACA PALUSTRIS 



99 



V 



i 



V 



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These experiments were done many times, with many plants and 

 always with the same result. Objection may be raised that 

 light passing through water is not quite the same as that obtained 

 by shading;' and to make sure, plants were grown under double 

 walled bell-jars with the space between the walls filled with 

 water, so that all Ho-ht 

 coming to the plants 

 had to pass through 

 2 to 3<=™ of water. 

 The behavior here 

 was precisely the 

 same as in the other 

 cases, i. e., if the 

 growing tip w^as in 

 the air, the air form 

 was produced, even 

 when the experiment 

 was conducted in 

 ^erj subdued light. 

 When conducted in 

 bright .sunlight' the 



only difference ob- Fig, 7. — Submerged plants in very good and very poor 



served 



\ 



was a more 



illumination. 



Vigorous growth. These experiments show that the illumination 

 neither directly, nor indirectly by any subsequent changes that 

 It may involve, can play an essential part in the stimulus to the 

 water form. 



One must hesitate before using this term. 



2. Nutrition. 



It is so very vague and indefinite that its chief advantage lies in 

 Its convenience in covering a mass of ignorance. It involves 

 the absorption and the use of oxygen, the absorption of carbon 

 dioxide, and the formation of carbohydrates, and hence the 

 action of illumination ; the formation of proteids and hence the 

 absorption of the various salts, also the migration of food and 

 other substances, and all the factors that control this, the toxic 

 and other effects of various ions which may be present. In 



