28o 



the red coloration. By artificial interference, a localized lack of moisture 

 and thereby a formation of anthocyanin is stimulated if the leaves of plants, 

 of which a red autumnal coloration is characteristic, be nicked or the 

 branches girdled. Then in the middle of summer a red color appears on the 

 upper parts above the injury. 



In regard to the phenomena of discoloration produced by heat and 

 drought, I will give some observations from 1892, in which year, in August, 

 unusually high temperatures occurred together with hot winds. I found on 

 the 19th of August a temperature of 52.7°C. on especially heavy loam soil. 

 All the plants wilted and the majority gradually lost their foliage. Naturally 

 great individual differences were also noticeable. 



The leaves became discolored and fell, the lowest leaves of the branches 

 being the first affected. 



In the Alder, the leaves fell without losing their green color. 



Acer Pseudoplatanus var. Schwedleri, the under side of the leaf is red. 

 From the tips backward the intercostal fields of the leaves turned a reddish 

 brown to leather color. Besides this, deep brown, perfectly dry rust spots 

 were scattered irregularly over the surface of the leaf. The injured leaves 

 remained in place. 



Acer Negundo. The upper leaves were somewhat flabby. The edges 

 of the leaflets were curled upward. The leaves next below were a pale yel- 

 lowish green, the lowest light yellow, uniformly rolled up on the dry edges. 



Acer plantanoides. The leaves show on their under side Dale yellow, 

 irregular, small rust spots running into one another and extending betv^een 

 the ribs. The dried tips bend upward like hooks. 



Fagus silvatica. On the various leaves, not always the lowest, but the 

 most exposed, were irregular, dry places with yellow, faded edges in the in- 

 tercostal fields. At times, the whole upper surface is equally lightly 

 browned. There is never any outlining of the edges. 



Vitis vinifera. At the beginning of the drought, among the normal 

 green leaves are found yellowish ones. The lemon yellow discoloration, red 

 in other varieties, begins at one place on the edge and advances into the 

 intercostal fields until only the veins seem green. In spite of the drought, I 

 found on various lower leaves the dry, angular spots of Plasmopara viticola. 



Prunus Persica. All the leaves are somewhat languishing, some (but 

 not always the lowest) turning yellow from the tips backward. On some 

 trees, the discoloration advances more quickly along the veins so that at first 

 the veining and then the rest of the" surface of the leaf colors yellow-red to 

 wine-red. Then the leaves drop. (Peculiarity of the variety). 



Prunus doniestica. All the leaves are flabby. The majority, however, 

 are still uniformly green with the exception of the lowest, which on many 

 branches have become a whitish yellow and have slender, brown, reflexed, dry 

 peripheral spots. Easily shaken off by the wind. 



Prunus avium. The lower leaves, especially on the short shoots 

 (brachyblasts), turn a uniform lemon yellow and fall. 



