460 



rule, wherever a brown coloration occurred, tannin was found in the cells. 

 The penetration of pyridine, like that of sulfuric acid, takes place chiefly 

 through the stomata. Very similar effects were found also, due to sub- 

 stances related to pyridine, such as picoUne, lutidine, nicotine, thiophene, etc. 



Phenol attacks the foliage very vigorously in aqueous solution as also 

 in the form of vapor, with strong plasmolysis and a brown coloration of the 

 protoplasm and chloroplasts. 



The blossoms behaved very differently in relation to fog; at times they 

 showed considerable difference in two varieties of the genus and, in fact, in 

 different petals of the same blossoms. Tulips, hyacinths and narcissus were 

 very resistant. 



It is interesting that, as a result of the lack of light connected with the 

 fog, whereby assimilation, transpiration and respiration are repressed, a 

 peculiar yellow-spotted condition often sets in. In this, there is an accumu- 

 lation of the acid content (because, with the decreased respiration, less 

 organic acids are burned) and an increase of turgescence connected with 

 this se>ems to lead to cell elongation in the mesophyll (aurigo). 



Thus, in considering the effect of fogs, we have to consider two injuri- 

 ous factors, the decreased light and the action of the poisonous substances. 

 This becomes the more dangerous the greater the plant's need of light. 

 Plants adjusted to a lesser supply of light (ferns) are less sensitive. 



Only in greenhouses can the injurious effect of such fogs be lessened, 

 and this has been done in England. Special purifying apparatus is made 

 use of (fog annihilators), with which the air entering the greenhouse is 

 passed over strongly absorbing substances (charcoal). For out of door 

 planting only a choice of resistant species can come under consideration. 



