128 



BOTANY FOR BEGINNERS 



CHAP. 



in and carbon dioxide given out ; but, the plant being in the dark, no 

 chlorophyll was produced and no assimilation could go on. 



(vi) This experiment shows that there is a loss of weight due to 

 respiration, caused by the oxygen uniting with some of the carbon of 

 the plant to form carbon dioxide. 



EXPT. 119. Place some germinating Peas in a funnel, as shown in 

 Fig. 148, so that they surround the bulb of a thermometer. Cover the 



apparatus over with a cardboard 

 box, and pass the thermometer 

 through a hole in the box. Note 

 there will be a rise of temperature, 

 due to the respiration which goes on. 



The Nitrogen of Plants. 

 In the water culture experiment 

 we found that the plant grown 

 in the solution without com- 

 pounds of nitrogen was stunted, 

 and soon died. It died from 

 want of nitrogen, though sur- 

 rounding it on every hand there 

 was plenty of free nitrogen. 

 Plants cannot use the free nitro- 

 gen of the air. Nitrogen must 

 always be presented to a plant 

 in a combined form. Most 



green plants obtain the nitrogen necessary for their growth from 

 the nitrates in the soil. Nitrates are mineral salts which 

 contain nitrogen ; they are found in all fertile soils. The nitrates 

 of the soil may be dissolved by water, which is subsequently 

 absorbed by the roots and is so introduced into a plant. 

 Parasites obtain the nitrogen necessary for their growth from 

 the hosts upon which they live. 



Carnivorous Plants are able to obtain the greater portion 

 of the nitrogen which they require for their growth from the 

 animals which they are able to entrap. 



The Sun-Dew (Fig. 150), which grows on the moors in Lanca- 

 shire, Yorkshire, North Wales, and many other parts of the 

 United Kingdom, is a good example of such a plant. The 

 name Sun-Dew has been given to the plant because, when the 

 sun shines, it appears to be covered with dew. The leaves are 

 covered with hairs called tentacles, on the end of which minute 



FIG. 148. Diagram illustrating the rise 

 of temperature due to respiration. 



