718 BOTANY. 
the contrary, they are always absorbed in the condition of 
compounds, as water, carbon dioxide, and the 
Nitrates Ammonia. 
Sulphates Potash. 
| Carbonates | o¢ Lime. 
Phosphates Iron. 
Silicates, or Soda, or 
Chlorides Magnesia. 
Of the last the nitrates of potash and ammonia, sulphate 
of lime, carbonates of ammonia and lime, are probably to 
be considered as the most important for ordinary plants. 
Water is necessary for all plants, and carbon dioxide for 
those which are green. 
149, In addition to the foregoing many organic com- 
pounds are absorbed in particular cases, as in those plants 
which live in decaying animal or vegetable matter (sapro- 
phytes), as well as those which absorb the juices from liv- 
ing plants (parasites). 
150. How the Food is Obtained —In the case of aquatic 
plants these compounds are taken into the plant-body by a 
process of diffusion from the surrounding water; in terres- 
trial plants the gaseous compounds, as carbon dioxide and 
carbonate of ammonia, are absorbed—at least in part—by 
the leaves directly from the surrounding air, while the 
solutions of these and the other compounds in the water in 
the soil find their way into the plant by diffusion. The 
water of streams and ponds and that found in moist soil 
generally contains, in addition to decayed vegetable matter, 
greater or less quantities of sulphate, carbonate, and phos- 
phate of lime, nitrates of potash and ammonia, besides small 
amounts of iron, silica, and chlorine. Plants flourish best 
when these constitute (in the aggregate) one part in one 
thousand parts of water. 
