394 PHYSIOLOGY OF GROWTH. 



parts of Ammonium nitrate, 0"2 parts of acid Potassium phosphate, 

 0'02 parts of Magnesium sulphate, and O'Ol parts of Calcium 

 chloride. Quantities of 50 c.c. of the fluid are placed in small 

 glass flasks, and treated respectively with 5 gr. (10 p.c.), 10 gr. 

 (20 p.c.), 25 gr. (50 p.c.) of grape-sugar. The vessels, stopped 

 with cotton-wool, are sterilised in the steam apparatus. For 

 observation we select Penicillium glaucum. The fluids are in- 

 fected with spores of this fungus, and then all exposed to the 

 same external conditions. It is found that development of the 

 fungus takes place even in the 50 p.c. solution, though certainly 

 it grows much more slowly in this than in the others. The causes 

 of the growth of the cells in fluids of high concentration is perhaps 

 to be sought in the fact that these act as stimuli, and so affect the 

 metabolism that an adequate elevation of the osmotic capacity of 

 the cell contents is produced. 2 



1 See H. de Vries, Untertuchnngen ilber die mechanischen TJraclien der Zell- 

 streckung, Halle, 1877, p. 56. 



2 See Eschenhagen, Einfluss von Losunjen auf das IVachsthum von Scldmmel- 

 pilzcn, Stolp, 1888. 



160. Respiration and Growth. 



As has already been pointed out in 108, some plants can grow 

 even in complete absence of free Oxygen. Most plants, however, 

 are only capable of growth when free Oxygen stands at their dis- 

 posal. This fact can easily be proved as follows. 1 Two retorts 

 of about 90 c.c. capacity (see Fig. 11) are filled with distilled 

 water, which has been boiled and then allowed to completely cool 

 again without exposure to the air. In each retort we place some 

 air-dry wheat grains or pea seeds, and then invert it with its mouth 

 under mercury. After twenty-four hours, when the seeds have 

 swollen, we replace the water of one retort almost entirely with 

 atmospheric air, that of the other with pure Hydrogen. This Ave 

 prepare by treating .Zinc free from Arsenic with dilute Hydrochloric 

 acid, and pass the gas through aqueous solutions of Potassium. 

 hydrate and Potassium permanganate, to free it from injurious 

 substances. In contact with the air the se^ds soon germinate ; in 

 Hydrogen, germination does not take place at all. If, however, the 

 seeds have not been kept too long in the Hydrogen (say only two 

 or three days), they germinate when subsequently exposed to normal 



