732 



pcarcd unchanged in form and position. Only later the green coloring 

 matter in the protoplasm was found to have changed and become a dirty 

 brownish green. Then the ground substances of the chl()roi)lasts united 

 with the other cell contents apparently leaving behind some granular 

 remnants. 



The ammonia might also exercise some special poisonous effect on the 

 cell contents besides combining with the acids as has been assumed in another 

 place. Kny' has already called attention to the fact that, according to the 

 statements quoted in the literature on this subject, the protoplasm in very 

 different parts of the plant possesses an alkaline reaction without having 

 influenced the chloroplasts. The same author has shown that a very dilute 

 ammonia solution injures the assimilatory activity. 



In one case, where the wall of a stable was used as the back wall of a 

 greenhouse, the way in which ammoniacal poisoning may often take ])lace 

 was clearly demonstrated. When the heat was turned on in the autumn, 

 ammonium carbonate developed from the wall, which, in a short time, 

 blackened the leaves of Aucuba, Viburnum Tinus, Pmuus Lauroccrasus, 

 the Dracaenae and other plants in the greenhouse. ( )nly the tissue immedi- 

 ately adjoining the veins of the leaves remained green. 



Tar and Asphalt Fume.s. 



The discoveries concerning the injuries of tar and asphalt fumes have 

 been explained only recently, since the material for ol)servation has become 

 more abundant. Aside from the effect which the asphalting of streets can 

 ])roduce at times in sensitive plants, the factories preparing the carbons for 

 arc lights are to be considered as essential causes of disease. 



Roses rich in tannic acid, strawberry leaves, Ampelopsis quinquefolia 

 and chestnuts should l)e named as the most important plants showing injury 

 from asphalt fumes-'. Different varieties of roses suffer in very different 

 degrees ; for example. Tea and Bengal Roses are less affected ; Remontants 

 and their hybrids, however, are for the most part very severely attacked. 

 Parts of the outer membrane, or the whole leaf surfaces become a dull l)lack. 

 Usually if the whole surface is not discolored (Fig. i68 la) the blackened 

 l)laces occur as interrupted or connected bands between the larger lateral 

 ril)S, that is, in the intercostal fields. If the sepals have been aft'ected by 

 the funics, the l)lossom buds unfold only poorly. Soon after the appearance 

 of the blackening, the contents of the epidermal cells of the upper side will 

 be found deeply browned, granular and lumpy, and usually deposited along 

 one of the horizontal walls. The cuticle is not browned and apparently 

 unchanged. When the leaf is more diseased, the epidermis of the under 

 side becomes affected in the same way and later collapses. On the other 

 hand, the mesophyll is but little irritated. The fumes act only on the exposed 

 surfaces of the organs; all the covered parts (Fig. i68 ib) remain un- 



1 Bot. Ccntralbl. 1.S9S, Vol. LXXIII, p. 430. 



2 Sorauer, P. Die Beschadig'un.sren dcr Vegetation durch Asphaltdampfe 

 Zeitschr. f. Pflanzenkrankli. 1897, p. 10. 



