42 



BOTANY. 



81. Food solutions which are too strong injure plants 

 instead of benefiting them. — In figures 27 to 33 are shown the 



results of some experiments 

 with strongly concentrated 

 food solutions. In this case 

 the food substance is potas- 

 sium nitrate. Solutions of 

 this salt of 2f , yfo, \of, and 

 20$ were prepared. Three 

 pots of pumpkin seedlings 

 were employed. In one the 

 soil (which was already quite 

 moist in all of the pots) was 

 saturated with the 2$, one with 

 the 10$, and the other with the 

 20$ solution. In a few hours 

 the seedlings in pots 31 and 32 

 had collapsed, while those in 

 pot 30 were still rigid. The 

 salt in 31 and 32, being, even 

 when diluted with the water in 

 the soil, stronger than the salts 

 in the cell-sap, withdrew water 



Pumpkin seedling removed from soil to show from the TOOt hairs, TOOtS, and 

 earth clinging to roots. frQm tfae j ower part of thg 



stems, so that the plants lost their rigidity. The lower part of 

 the stems was flabby. The plants were then photographed as 

 shown in figures 30-32. Some of the 5$ solution was then 

 added to pot 30. In four hours (at 6 p.m.) two of the seed- 

 lings showed signs of collapse. On the following morning 

 these two had collapsed, and the photograph of the result is 

 shown in figure ^^. 



Synopsis. — Plants obtain their food either in a liquid or a gaseous form. 

 Plants obtain their liquid food (mostly certain mineral and nitrogenous 

 substances) by absorption. 



