319 



green and form no starch. They also do not recover, if the branch is 

 brought back to air containing carbon-dioxid, but go to pieces after a short 

 time. It thus becomes evident that each leaf has its independent existence 

 and that any disturbance of it cannot be adjusted by the organism as a 

 whole. The organ which has become functionless is thrown off from the 

 body. 



B. EXCESS OF WATER AND NUTRITIVE SUBSTANCES, 

 a. Excess of Water. 



MOISTURE. 



The phenomena of yellowing and decomposition connected with stag- 

 nate water have been considered when discussing the disadvantages of heavy 

 soils. We are thus concerned here only with proving by example, how an 

 excess of water, like a lack of it, retards production. Thus Stahl- 

 Schroeder's^ experiments with oats in sterile sea-sand to which the nutrient 

 solution had been added, gave the following results. With the addition of 

 water there were produced : 



Thus only the vessels containing a medium amount of water yielded a 

 good harvest in grains. With a larger water content, the harvest of grains 

 fell, while the yield in straw increased. With a lack of water in the sand 

 (35 per cent.) and with an excess (95 per cent.) none of the grains ripened. 

 The poorer the growth of the plants, the greater their percentage of ash con- 

 tent, and wealth of phosphoric acid and nitrogen. 



Clogging of Drain Tile. . 



Wherever flat lying drains extend through the root systems of perennial 

 plants, an unusually luxuriant root growth may stop up the drains. The 

 long whip-like, very slender and comparatively thin roots lying side by side, 

 like cords, in this way form mats ten or more meters long and as thick as 

 the width of the drain allows. The most dangerous tree seems to be the wil- 

 low for most of the drain mats seem to be formed by it, yet all plants may 

 form similar root-growths and Magnus- once found, for example, the 

 rhizome of the horse tail (Equisetum palustre, L.) growing very luxuriantly 

 in such a mat. Cohn^ found a drain mat which came from a pipe laid 125 



1 of. Biedermann's Centralbl. f. Agrikulturchem. 1905, Part 2. 



2 Sitzungsber. d. Bot. Vereins vom 26 Mai, 1876. Vol. XVIII, p. 72. 



3 Verh. d. schles, Gesellsch. f. vaterl. Kultur, 25 Oktober, 1883. 



