393 



of acid associated unth an excess of nitrogen may also be sought elsewhere 

 and may be the cause of the rapid appearance of bacterial decay^ 



In the Cucurbitaceae (cucumbers and melons) a concentration of the 

 nutrient solution, not dangerous in itself, can act injuriously if the temper- 

 ature is continuously too low. In this case gum appears most abundantly 

 on the iruit and connected with it a blackening of the ducts is also noticed. 



In tobacco culture, an excess of nitrogen manifests itself in coarser 

 leaves and a larger nicotine content^. 



Mention has been made of the fact that sewage fertilization of grain 

 may cause lodging and sterility. 



Excessive Nitrogen Fertilization for Decorative Plants. 



Very numerous cases of this may be found. Besides fertilization with 

 sewage and Chile saltpetre, or ammonium sulfate, horn shavings are ex- 

 tensively used, especially for garden plants. Naturally we can cite only a 

 few examples. 1 gave a few plants of Begonia semperflorens an excess of 

 ammonium sulfate. Four days after fertilization the young shoots became 

 discolored at the base and began to drop. The edges of the leaves began 

 to show dirty green areas which later became brown and dried up. These 

 were connected with the healthy tissue at the centre of the leaf by 

 a more transparent transitional zone. In the sun, the wilting became more 

 rapid. The pith and bark were found to be filled with masses of calcium 

 oxalate ; the individual crystals were not as sharp as those in healthy speci- 

 mens but more rounded like tubers. No starch was present in the diseased 

 tissues and the chloroplastids were reduced to small angular grains. 

 The ducts were frequently filled with a brown, granular content. The cell 

 walls of all the tissues were brown. The contents of the epidermal cells of 

 the leaves were brown and granular. Before the decomposition of the 

 chlorophyll grains, brown drops were often found in the contents of the 

 mesophyll cells. 



In Begonias, as well as in Pelargonium sonale, the leaves discolor and 

 fall off easily wnen dried. I found an unusual number of calcium oxalate 

 crystals in the pith and young bark of the axes of diseased plants. The 

 stems of the Pelargoniums contained in general fewer and smaller starch 

 grains. They were almost entirely lacking in the bark parenchyma, while, 

 in the over-fertilized plants, they were present in abundance. 



This is an example of the same phenomenon observed in potatoes and 

 beets, — i. e., a poverty in carbohydrates. 



A slight fertilization with Chile saltpetre, given to freshly rooted Pelar- 

 gonium cuttings at first caused a very luxuriant growth. Later, because of 

 frequent repetition, the effects became serious; — the leaves drooped, and 

 brown decayed areas appeared on the stem just above the leaf bud. In a 

 a short time these spots encircled the entire stem. Then the leaves fell and 



1 See Action of oxalic acid, p. 361. 



2 Schellmann, W., Der Tabak und seine Nahrungsanspriiche. "Der Pflanzer." 

 Herausg. Usambara-Post 1905, No. 5. 



