28l 



Pruniis Cerasus. Only a few leaves turn yellow, otherwise the entire 

 foliage is still fresh. A proof that the cherry loves drought. 



Pirns communis. According to the exposure rust spots are found in 

 greater or less numbers showing, however, no yellowing. At times dry areas 

 appear on the edges of the leaves, but more frequently the whole surface is a 

 dark umber brown (the under side lighter in color with a still fresh green or 

 lightly brownish mid-rib). The edges strongly rolled upward. Because the 

 petioles remain green, the injured leaves do not fall at all or only much 

 later. 



From these and numerous other observations it is evident that, on an 

 average, the parts of the leaves furthest from the veins discolor and dry first 

 and most. When periods of heat follow one another rapidly with a strong 

 sun action, the rust spots become very conspicuous ; with a lesser intensity of 

 the sunshine, a general discoloration in the form of spots prevails. 



Here belongs also the especially strong development of anthocyanin in 

 dry, poor locahties, which becomes noticeable even in the arctic regions, 

 where the red coloration with the strong illumination is a prevailing 

 phenomenon. Wullt^ cites a very characteristic example. He found in 

 places, fertilized by the excreta of birds, that the formation of anthocyanin 

 disappeared in plants of which the vegetative organs seemed strongly redden- 

 ed in arid regions. 



Finally, there must be considered the decrease in the power of move- 

 ment of clover leaflets and related organs, with a continued lack of moisture. 

 In Mimosa pudica the periodic irritabihty is lost and the leaflets remain 

 open, — "drought cramp." 



The Red Coloration in Grain. 



The red coloration in grain in continued dry, hot summers has often 

 called forth the theory that parasitic influences participated in it. Klebahn- 

 tested more closely a special case, which was universally striking because of 

 its wide distribution and intensity. He found that the red coloring matter 

 appeared gradually in place of the cholorophyll. While the alcoholic ex- 

 tract of normal leaves appears green, it is colored only slightly yellow in red 



1 Wulff, Thorild, Botanische Beobachtungen aus Spitzbergen, Lund. 1902. In 

 regard to the theory at present generally held that anthocyanin is said to form a 

 protection for the chlorophyll against an excess of light, Wulff (p. 67) calls attention 

 to Engelmann's investigations from which it is evident that the light absorption of 

 the red anthocyanin is complementary to that of the chlorophyll and accordingly 

 does not retard the decomposition of the carbon dioxid. "This fact has moreover 

 proved most fully the untenability of the Pringsheim-Kny-Kerner theory of pro- 

 tection from light." Wulff sees the advantage of the anthocyanin in its greater 

 storage of heat. As I have mentioned already, I am unable to accept the above 

 utility arrangements or the expressions of a "finality" in the organism and I per- 

 ceive everywhere the necessary phenomena resulting from definite combinations of 

 the factors of growth. The formation of anthocyanin seems to me to be the result 

 of an excess of light on the cell content, rich in free acids, at the disposal of which 

 there is no assimilate containing sufficient nitrogen. This condition can be pro- 

 duced, as in plants of cold regions, by a lack of heat; in other cases by a scarcity 

 of water, a decreased supply of nutriment, etc. 



2 Klebahn, H., Einige Wirkungen der Diirre des Friihjahrs 1893. Zeitschr. f. 

 Pflanzenkrankh. 1894, p. 262. 



