372 E. E. GAERTNER 



the most. Mikola (1950) in data from several hundred Scots pine and spruce 

 (Picea abies (L.) Karst.) in central Finland, showed that in the 1 8 years of 

 agricultural crop failure since 1800 there was a correlation between these 

 failures and tree growth, wherever crop failure was due to excessive 

 moisture or frost (resulting in a cooler summer), but not where drought 

 caused failure. Duruag these 1 8 periods the radial growth of these two species 

 averaged 18% less than the growth in the preceding year. The floods in 

 the marshy forests near Gabcikovo in July 1954 were described by Farsky 

 (1957). Most of the younger plants were killed and the older ones lost their 

 leaves when the flood water became warm and stagnant. Those species 

 most severely affected included Fraxinus excelsior, Quercus rohtir, Robinia 

 pseudoacacia, Primus avium, Tilia cordata, Aesculus hippocastanum znd Acer spp. 



Finally, Day (1946), commenting on root diseases in conifers, suggests 

 that fungi might be of secondary importance as compared to adverse soil 

 conditions of both drought and water-logging, which stimulate abnormal 

 root growth consisting of unhgnified collapsed tracheids. On a lesser scale, 

 excess of seasonal moisture at Chalk River, Ontario, was found to retard 

 growth of yellow birch {Betula lutea Michx, f ) (Fraser, 1956, 1961). After 

 extensive flooding in New Orleans, Bonck and Penfound (1944) measured 

 terminal growth in two species of willow, sand bar willow [Salix interior 

 Rowlee) and black willow {Salix ni^ra Marsh), pecan (Crtryrt ilUnoensis 

 (Wang.) K. Koch) and hackberry [Celtis mississippiensis Bose). They have 

 recorded that these species grew more rapidly during the April flood than 

 at any other sector of their growth period, but elongated very little during 

 the June flood. It is probable that the floods had Uttle or no effect on the 

 normal growth pattern of any of the four species studied. 



It has been stated (Russell, 1932) that an occasional extreme drought might 

 affect vegetational boundaries more than normal climatic conditions. Late 

 spring drought in Pennsylvania in 1935 and 1936 appeared to have caused 

 stunted terminal growth and shorter needles in white pine (Craighead, 

 1941). Day (1950) on the other hand has found no injury to pine, but 

 cracking of the stem, or dieback of younger trees of Sitka [Picea sitchensis 

 (Bong.) Carr.) and Norway spruce [Picea abies (L.) Karst.) after a drought 

 during the growing season in Wales and Scotland. These drought cracks 

 result from internal shrinkage or collapse of wood as the water is with- 

 drawn from the main stem and occur only in trees which are about 20 years 

 old. The affected spruces were distinguished by low specific gravity of the 

 wood produced and the marked absence of well-thickened late wood. A 

 partial death of the root system appeared to be comiected with the condi- 

 tion, wliich occurs on fertile but shallow soil where the rooting space is too 



