30I 



veins together with the immediately adjacent tissue remain green. Finally the 

 leaves dry up, beginning usually at the edges, with a dark brown color (see 

 the adjoining Fig. 39). Flower and fruit formation are scanty. With a lack 

 of potassium, not infrequently, individual plants go to pieces prematurely'^ , 

 while, with a lack of nitrogen and phosphoric acid, even the smallest plants 

 can be maintained until the end of the time of growth. 



Of especial importance is the observ^ation of the above-named authors, 

 that the roots as well as the tubers of plants grown with a lack of potassium 

 tend very easily to decay .and that plants lacking any nutritive substance 

 are always more predisposed to attack from animal and vegetable parasites. 



Von Feilitzen- made the same observ^ation on timothy grown on moors. 

 It was attacked by fungi only after it had been weakened by a lack of potas- 

 sium. He noticed in clover that the lots sown without potassium, or with 

 a slowly soluble compound of it, were "scorched" as if grown on poor 

 sandy soil, after long periods of drought. 



When experimenting with different fertilizers, MoUer found that with 

 a lack of potassium the seedling plants of the Scotch pine had less growing 

 power, their needles had a faded appearance. 



Valuable as are these attempts to find positive characteristics due to a 

 lack of potassium, I still think that for a long time we will have to make use 

 of these characteristics only with great care in diagnosis. In the first place, 

 we do not know whether the same characteristics always, — i. e. with all vari- 

 ations of the factors of growth, — become visible in the same species. In the 

 second place, we still know too little of the phenomena of starvation which 

 make themselves felt with other nutritive substances. In the third place, the 

 influence of injurious gases at times gives such deceivingly similar effects, 

 aside from parasitic attacks, that it might be difficult to draw definite con- 

 clusions from the changes in habit alone. It should be taken into consider- 

 ation that almost all injuries to the leaf manifest themselves first in the 

 regions lying farthest away from the veins conducting water, hence the fre- 

 quent beginning of the diseased condition at the edge of the leaf or in the 

 middle of the intercostal areas, upcurved between the larger veins. 



d. Changes Due to a Lack of Calcium. 



It is well known that the plant uses calcium as stiffening for the cell 

 walls and as a means for combining the poisonous oxalic acid produced. 

 In the phenomena of disease, the fact that an excess of oxalic acid can re- 

 dissolve small amounts of calcium oxalate is important^. The calcium oxa- 

 late produced is re-dissolved only in a few cases*. Usually the organism 



1 Compare also, v. Seelhorst, Die durch Kalimange] bei Vietsbohnen (Phaseolus 

 vulgaris nanus) he7vor.e:erufenen Erscheiniinsren. Zeitschr. f. Pflanzerkr. 1906, p. 2. 



- V. Feilitzen -Jonkoping', Wie zeigt sich der Kalimangel bei Klee und Timothee- 

 gras? Mitt. d. Ver. z. Ford d. Moorkultur 1904. No. 4. n. 41. 



3 "Wiiitz, Dictionaire de chimie II, p. 647, cit. by de Vries in Landwirtsch. Jahrb. 

 1881 p. 81. 



4 Sorauer, P., Bertrage zur Keimungsg-eschlchte der KartofEelknolle. Berlin. 

 Weigandt & Hempel. 1868, p. 27, and de Vries, H., tjber die Bedeutung der Kalkab- 

 la.gerungen in den Pflanzen. Landwirtsch. Jahrb. v. Thiel, 1881, p. 80. 



