WATER CULTURE, PHOTOSYNTHESIS; RESPIRATION. l9l 



(d) About one-fourth fill a cylindrical jar with lime- or 

 baryta- water, then push into the jar, well above the liquid, 

 a piece of gauze to support some germinating seeds and 

 blotting-paper, and cork tightly. During several days 

 note the gradual whitening of the reagent, which should 

 be gently shaken from time to time. Set up a similar ap- 

 paratus without the seeds, as a control. 



(e) A striking and roughly quantitative experiment may 

 be arranged as follows, taking the composition of air as 

 20 per cent, oxygen and 80 per cent, nitrogen. Get three 

 similar J -tubes ; to graduate one tube and from it the 

 others into fifths, cork the short arm, fill the tube 

 with water, pour the water into a measuring glass, and as 

 each fifth part of the water is poured back into the tube 

 mark the level by a file scratch. Into the short arm of 

 each tube place six soaked Wheat seeds, with a wad of 

 wet cotton to keep them moist, and cork tightly. Take 

 three narrow jars or large test-tubes, a little wider than 

 the J -tubes, and place in them (A) caustic potash, (1?) 

 pyrogallate of potash, (C) water ; into each dip the long 

 arm of one of the inverted J -tubes. If test-tubes are used 

 for the reagents, support them in a stand. 



In B the reagent (pyrogallate) quickly rises in the tube 

 to about the first fifths-mark, and the seeds germinate very 

 little; in A the reagent (potash) rises gradually and to 

 the same extent, while the seeds germinate quite well ; in 

 C the water hardly rises at all, though germination occurs 

 as in A. What has happened in each case, and what in- 

 ferences may be drawn from the observed facts ? 



(/) Suspend three healthy laurel leaves by threads from the well- 

 fitting cork of a large bottle containing lime-water, and expose 

 them to bright light. After several hours the lime-water is still 

 comparatively clear. Cover the bottle with black cloth, and in a 

 few hours the lime-water will become quite milky, owing to the 

 respiration being no longer masked by the re-assimilation of the 

 carbon dioxide it produces. 



(g) Place some green leaves in a glass jar (Fig. 44), through which 

 a slow current of air is passed. This air is deprived of its carbon 

 dioxide by the potash contained in the U-tube, so that the lime- 

 water or baryta-water in both bottles remains clear so long as the 

 leaves are exposed to sunlight or very bright daylight, whereas if the 



