670 



extensive disturbances. It is probable that a further decomposition will 

 introduce phenomena of decay which produce the best nutrient substrata for 

 parasites and saphrophytes. The asparagin is worked up well by the fungi 

 in the presence of sugar. VogeP found in the germination of moistened 

 cress seed that hydrogen sulfid was produced in the dark, while, in check 

 experiments, in lighted places, the lead paper showed practically no change. 



A different process may prevail in the leaf parenchyma from that in 

 the leaf veins. In young Dahlia plants Borodin" proved the presence of 

 saltpetre in the veins and in the petioles, but large amounts of tyrosin and 

 no saltpetre in the leaf parenchyma. Here the tyrosin may well be no 

 analytic product but rather a synthetic one; for if the young shoots of 

 dahlias become etiolated, no tyrosin is formed, but asparagin, which does 

 not appear when the plants are grown in the light. 



At times, at any rate, an increase in proteins is found in the dark but it 

 is then caused by the very abundant carbohydrates at the jDlant's disposal in 

 the stores of reserve substances, as IwanofT^ has shown, for example, fot 

 Allium Cepa. If carbohydrates are present, the leaves, even in the dark, 

 can change the nitrate nitrogen into protein nitrogen, as Zaleski'* found in 

 the leaves of Helianthus, which had been placed in a nutrient solution con- 

 taining nitrates and sugar. 



We have stated here simply a series of facts which show the natural 

 changes in the plant body due to a lack of light. These explain sufficiently 

 the decreased power of resistance of the shaded plant parts through atmos- 

 pheric influence,, as well as parasitic attacks.' 



1 Vogel, Ein aufCallig-er Unterschied zwischen Keimen am Tagreslicht iind im 

 Dunkeln; cit. Bot. Jahresber. 1877, p. 675. 



2 Sitszungsber. d, Bot. Sekt Petersburg-. Naturf. Ges. 1881; cit. Botan. Zeit. 

 1882; p. 589. 



3 Iwanoff, M., Versuche iiber die Frage, ob in den Pflanzen bei Lichtabschlu.ss 

 Eiweissstoffe sich bilden. L/andw. Versuchsstationon 1901, p. 78. 



•t Zaleski, W., Die Bedingungen dor ]i;iweiss])ildung in den Pflanzen. Charkow 

 1900 (Russian); cit. Bot. Centralbl. 1901, Vol. 87, p. 277. 



