300 



Agriculturally worth consideration is the fact, confirmed experi- 

 mentally*, that with a lack of potassium, as contrasted with complete nu- 

 trition, a larger part of the nutritive substances taken up (excepting the 

 [ihosphoric acid) will wander back into the soil at the time of ripening. 

 This was observed, at least, in summer wheat, barley, peas, and mustard. 

 Potatoes formed an exception. 



The manifestation of a lack of potassium in fungi is very interesting. 

 Molliard and Coupin- found in Sterigmatocystis nigra a malformation of the 

 conidia which were produced only very exceptionally and matured incom- 

 pletely. As under other conditions due to starvation, the conidia germi- 

 nated at once, but their contents grew into a chlamydospore form. 



The most important question for agriculture is, whether positive ex- 

 ternal cliaracteristics may be found which indicate with certainty the lack of 

 potassium? 



We owe the most important experiments along this line to Wilfartli 

 and Wimmer'', who set up comparative cultures of sugar beets, potatoes 

 buckwheat etc. They tested also for scarcity of nitrogen and phosphoric 

 acid and found that Avith a lack of nitrogen leaves took on a light green 

 to yellowish coloration and finally dried up with a light brownish yellow color. 

 With a lack of phosphoric acid they were colored a deep, dark green, cor- 

 responding to the occasional excess of nitrogen, and in extreme cases black- 

 ish brown spots were formed at the edges and later distributed over the 

 entire surface of the leaf, which sometimes had a reddish color at first. 

 Finally followed a drying up accompanied by a dark green to a blackish 

 brown coloration. If, however, sufficient potassium lay at the disposal of 

 such starved plants, abundant quantities of starch and sugar were formed 

 in spite of this ; even with a lack of nitrogen, this process seems to be in- 

 creased rather than decreased. If, however, in an otherwise normal nutri- 

 tive supply, the potassium is lacking, the above-mentioned increased forma- 

 tion of straw in grain as against the formation of kernels becomes manifest. 

 Under these conditions the amount of green growth in edible roots, or 

 tuberous plants, was increased in proportion to the containers of the reserve 

 substances, which possessed appreciably less carbo-hydrates tlian with a 

 lack of nitrogen and phosphoric acid. 



Since the plants use first of all the potassium supply in building their 

 vegetative skeleton, they retain longer, by their habit of growth, the appear- 

 ance of normally nourished plants with a lack of potassium than with a 

 lack of nitrogen and phosphoric acid, but then the internodes are shortened 

 and the leaves curl upward convexly. At first near the leaf edges and then 

 later scattered over the whole surface of the leaf, appear yellowish spots 

 which rapidly turn brown or often change to white, while the petioles and 



1 Wilfarth, Romer and "Wimmer, tJber die Nahrstoffaufnahme der Pflanzen in 

 verschiedonen Zeiten ihres Wachstums. cit. Centralbl. f. Agrik.-Chemie 1906 p. 263. 



2 Molliard et Coupin, Sur les formes teratologiques du Sterigmatocystis nigra 

 prive de Potassium. Compt. rend. 1903. CXXXVI p. 1659. 



•'' Wilfarth, H. W. and "Wimmer, G. (Ref.) Die Kennzeichen des Kalimangels 

 an den Bliittern der Pflanzen. Zeitschr. f. Pflanzenkrankh. 1903 p. 82. 



