EFFECTS ON PLANTS 9 



segments or individual cells; cells shorter, and more turgid, with bulging ends. 

 Atrophy of the cytoplasm and chlorophyll bands occurs, and changes in the fat 

 content, cell-sap, etc. may appear. Molliard and Coupin ('03) found that when 

 Sterigmatocystis (Aspergillus) niger is grown in the absence of potassium, the 

 normal form of the conidial apparatus disappears, variable outgrowths replacing 

 the normal conidiophores. Prothallia of Gymnogramme sulphurea are able to 

 grow and form chloroplastids with only traces of potassium present, but no 

 starch is formed. In cells of Hydrodictyon and Basidiobolus ranarum on K-free 

 media, the cytoplasm becomes abnormally vacuolated and the nuclei indistinct. 

 In Zygnema filaments the pyrenoids rapidly lose starch, the chloroplasts becom- 

 ing vacuolated and the radiating strands of protoplasm disappearing. In 

 Spirogyra cells kept in K-free solution, after 35 days no mitosis occurs, although 

 both cells and nuclei undergo preliminary elongation. The inhibition of mitosis 

 cannot be attributed to the lack of potassium in the nucleus, however, since 

 Macallum ('05) has shown that potassium is normally absent from the nucleus 

 in both plant and animal cells. 



Reed, in agreement with previous investigators (see literature reviewed 

 by him), found that in some cases the function of potassium can be partially 

 accomplished by the substitution of sodium. For example, when a subminimal 

 amount of potassium is present, some evidence indicates that certain moss-spores 

 can germinate and utilize sodium during the embryonic stages of development. 

 Dassonville ('98) found that the substitution of sodium for potassium in the 

 wheat plant produces less growth but more lignification; in the secondary roots 

 of the tomato certain characteristic histological changes result. 



MAGNESIUM DEFICIENCY 



Although von Liebig ('76) and earlier investigators recognized that magne- 

 sium is essential for the growth of the higher plants, its function long remained 

 somewhat obscure. Loew ('92) thought it served as a carrier for phosphoric acid 

 in the formation of nucleoproteins. Willstaetter ('06) has proved that magne- 

 sium is a constituent of the chlorophyll molecule. Numerous investigators 

 have noted the antagonistic action of magnesium and calcium (literature 

 reviewed by Reed), including possibilities of their substitution for each other 

 in some cases. 



Von Raumer ('83) noted in Phaseolus multiflorus deprived of magnesium a 

 stunted growth of stem and leaves, with unhealthy chloroplasts. He con- 

 cluded that magnesium is essential for starch transportation. Bokorny 

 ('95) with magnesium deficiency in various algae likewise found modifications 

 of the chloroplasts, with markedly decreased size of nuclei. Reed ('07) observed 

 that the ratio of magnesium and phosphorus is an important factor in spore 

 formation in Aspergillus niger, and in Vaucheria the oil droplets disappear in 

 Mg-free cultures. In Spirogyra, the chloroplasts become, variably disarranged 

 and retracted into an irregular cytoplasmic mass near the center of the cell, 

 although the pyrenoids and nuclei appear unaffected. Mitosis is still possible- 

 though greatly retarded. According to Dickson ('18), a deficiency of magne, 



