lo6 BOTANICAL GAZETTE [august 



»J 



from it must occur. In a large number of experiments consid- 

 erable variation in this respect was noticed. Some plants when 

 transferred from the air into a moist chamber showed little 

 change, while others developed leaves somewhat intermediate 

 between those and the water leaves. , Some, where extra pre- 

 caution to keep the atmosphere as near saturation as possible 

 and free from changes of temperature, produced essentially the 

 water form, as in fig, lo. The lobes are not so long, but the 

 form is the same. In the case of plants grown from seed in 

 moist chambers, several have reached as many as thirty-five 

 internodes and are still producing water leaves. In these cases 

 the amount of CO^ and O^ is the same as if the plants grew in 

 the ordinary atmosphere, so that here, at least, differences in the 

 amount of these gases cannot be any part of the stimulus to the 

 formation of the water form. 



The essential feature common to the water and the moist air 

 is the inhibition of transpiration and the consequent choking 

 of the cells and diluting of the protoplasm with water. This 

 can be tested in another way, /. ^., by growing the plants entirely 

 under water and at the same time drawing the water out from 

 the protoplasm; or in reality causing evaporation, or transpira- 

 tion, by means of high osmotic pressure. Plants producing 

 water leaves were placed in nutrient solutions of a strength not 

 quite sufficient to plasmolyze them ; also in very dilute solutions 

 made up to the same osmotic pressure with KCl and also 

 Ca(N03)2. These were allowed to evaporate down, becoming 

 gradually stronger. When they reached a strength of solution 



equal to about a ^ N salt solution the water leaves ceased to 



form and the air type of leaf appeared. This shows that even 

 under water, if sufficient water be drawn from the protoplasm, 

 the air leaf will be formed. As the amount of light, COg, and 

 Og is the same here as in the water, and the water type is not 

 produced, it is evident that these form no part of the stimulus 

 to the formation of the water form. Further experiments along 

 this line are still in progress, with other salts and also with non- 

 electrolytes. 



