731 



become free that they produce injuries, although the plants in general are 

 found to be very resistent. The sensitiveness of different species varies 

 greatly, but the kind of injury shows a great uniformity; namely, a black 

 coloration occurring in spots or surfaces. 



Experiments made by Borner, Haselhoff and Konig^ exhibited in the 

 oak the appearance of dark spots or a complete blackening of the leaves. In 

 the cherry at first a brown color was seen and later black. After a short 

 exposure to the action of ammonia the leaves and blades of barley were 

 bleached white on the side turned toward the sun. Rye and wheat showed 

 rusty spots and edges. 



In addition to the cases already known in literature, I will add here a 

 few of my own observations. I found the leaf tips of barley turning white. 

 The intercostal fields of young chestnut leaves were dark at first, but became 

 black the next day and later dried up. The foliage of some of the red blos- 

 soming varieties of Azalea indie a behaved similarly, while in a variety stand- 

 ing nearby but bearing white blossoms only a browning of the leaf tips and 

 edges appeared. Along the edges of the outermost tips of blossoms of the 

 red variety, white, nearly round, or wedge-shaped spots resembling a natural 

 variegation were found, while blossoms of the white variety within the same 

 length of time remain unchanged with the exception of scattered small, 

 brown spots. No after effects could be perceived after the plants had been 

 removed from the ammonia atmosphere ; but there was some reaction in the 

 inflorescence of a cineraria. The red, outer blossoms which had turned blue 

 from the ammonia, became red again some time after their removal from 

 the ammoniacal atmosphere. 



The spruce furnishes an example of the influence of the developmental 

 stage on the amount of injury. The old needles took on a pitch black color 

 and were retained, while the color tone of the young, delicate needles, at first 

 a dirty green, later passed over into a faded, reddish yellow. The individual 

 power of resistance in the different needles is shown especially clearly in an 

 experiment hi which some needles could be observed on branches, among 

 the pitch black ones, which showed noi discoloration or at most only a 

 darker green. The black color was due mainly to the pitch black color tone 

 which the protoplasma of the epidermis and mesophyll cells had assumed. 

 The cell walls were only slightly brown. In the cells most injured the 

 contents had become a consistent, granular, doughy mass, which at times had 

 drawn back from the walls. The contents of the guard cells of the stomata 

 were also pitchy black, never red, as in injuries due to acids. In the transi- 

 tional places between tissue which had remained healthy and that which had 

 blackened, it was noticed that the protoplasmic mass in which the chloro- 

 plasts were imbedded had already turned black, while these granules ap- 



1 Zeitschr. f. Pflanzenki^ankh. 1893, p. 100. Lindau (loc. cit., p. 286) describes 

 the action of the strongly concentrated ammonia gas on the phmt cell; in the 

 interior of the leaf the cells usually show very strong- plasmolysis; the contents 

 become indistinct and at times drops of oil are exuded. In this a brown to black 

 coloring matter is given out which tinges the entire contracted conti-nts. This 

 proves later to be a ferment. 



