284 



ing this disease from others. With reference to the form of "Red Scorch," 

 described in the second volume of this manual and caused by Fseudopeziza 

 fracheiphila (see Vol. II., p. 278*) in which the discoloration often begins in 

 the form of spots in the angles of the veins, it should be emphasized here 

 that the leaf scorch, which is due to a lack of moisture together with strong 

 sunshine, begins as a rule with a discoloration of the intercostal fields start- 

 ing from the edge. The phenomena vary greatly, according to the variety 

 and habitat, and at times only a shining yellow color is found instead of the 

 reddening. The edges of the leaves often dry up. The kind of discoloration 

 runs parallel with the progress of the summer blight in other woody plants, 

 whereby it may usually be observed how the deficient moisture supply be- 

 comes evident at first on the parts lying furthest away from the petioles and 

 the mid-rib and then advances until finally only the immediate surroundings 

 of the veins remain green. (See Changes due to place of growth.) 



In regard to the physiological activity, Miiller-Thurgau had proved 

 earlier that the formation of starch and its solution took place the more 

 slowly, the less the water content of the leaves^ ; irrigated vines formed more 

 sugar. 



A phenomenon manifesting itself like the parasitic scorch has been de- 

 scribed by Sauvageau and Perraud- as the pectin disease (maladie pectique), 

 the result of continued drought. In this, the leaf blades are loosened from 

 the petiole. 



Yellowing Due to the Grafting Stock. 



In our species of fruit there is often a lack of water, because a rapidly 

 growing variety grafted on a dwarf stock, in times of great evaporation, is 

 not able to convey the necessary water to the graft. 



On good soils pears, grafted on quince stock, often turn yellow, while 

 trees on wild stock thrive well. In Avy summers I found with such dwarf 

 trunks that well grown scions, inserted later in the bark, formed strong but 

 j^ellowish shoots, while the older top was green. In this too I see phenomena 

 of the lack of moisture due to the quince stock which (especially if planted 

 shallow) cannot obtain the necessary water. Pears on shallow planted 

 quinces ripen their foliage more quickly and lose it earlier. 



Premature Drying of the Foliage. 



When the foliage dies as a result of the summer drought, in which it 

 usually hangs on the branch, because the petiole has remained fresh, the 

 injury suffered by the tree is far greater than is generally understood. 



It is thought that the injury consists primarily in the premature stopping 

 of leaf activity and the lessened formation of wood. Kraus'^ investigations 



* Paging in the German originaL 



1 III. .lahresber. d. A^ersuchsstat. Waden.sweil. Zi'rich 1894. p. 56. 



2 Sauvageau. C. et Perraud, J., La maladie pectique de la vigne. Revue de 

 viticulture 1894, p. 9. 



3 Bot. Zeit. 1873, Nos. 26 and 27. 



