CHAPTER VI. 



Fog. 



In temperate climates, complaint is rarely heard of injuries from fog. 

 In the mountains, vegetation has adjusted itself to the abundant precipi- 

 tation and the attempt has been made so far as possible to overcome the 

 delay of ripening grains and of drying the remaining vegetable produce by 

 cultural regulations. 



The so-called "fog holes" of the plains may also be "frost holes." 

 These are distinguished by a vigorous lichen growth on the tree trunks. 



In warm regions, fog becomes a more important factor, causing damage 

 to plants, since it actually favors the development of saprophytic and 

 parasitic fungi. We find the greatest number of complaints in regions 

 where cotton is grown and exhaustive descriptions have been sent from 

 Egypt. David^ writes from the cotton experiment station at Zagazig that 

 each October morning in lower Egypt, the soil is covered by heavy, thick 

 vapors or low fogs. The first general result is that the bolls do not open 

 because the carpophyles remain too tough. The foliage becomes covered 

 with red spots, ascribed to the action of the sun on the dew drops, acting as 

 lenses. The cotton fibres in the bolls decay and lose their value from the 

 action of a black fungus. Besides cotton. Hibiscus esculantus and H. 

 cannabinus also suffer; young maize plants as well. The irrigation with 

 Nile water, its soaking through the land while the soil is fallow, makes it 

 moist, dense and slimy or oozy. This physical characteristic is the chief 

 factor which makes Egyptian fogs more disastrous than the English and 

 mountain fogs. 



The sensitiveness of cotton is due to its special soil and climate needs. 

 These are very thoroughly described in Oppel's- special work. According 

 to this, cotton as a low-land plant cannot endure a stony soil or any abrupt 

 changes in temperature. In its time of growth, lasting six months, it 

 requires i8° to 20°C. a medium heat and abundant moisture, but it is found 

 to be very sensitive to continued rain. "A high degree of atmospheric 

 warmth, a good deal of soil warmth, a clear sky during the day and abundant 



1 David, Nebel und Krdausdiinstung-en und ihr Einfluss auf agyptische Baum- 

 wolle. Zeitschr. f. Pflanzenkrankh. 1897, p. 143. 



2 Oppel, Die Baumwolle nach Geschichte, Anbau, etc. Leipzig', cit. Bot. 

 Jahresber. 1902. I, p. 374. 



