ASSIMILATION AND GROWTH. 21 



II. THE GAIN IN SUBSTANCE BY ASSIMILATION, AND THE Loss OF SUB- 

 STANCE DURING GROWTH. 



Select a number of beans (Windsor, Horticultural, Lima, or 

 white), of nearly the same size, weigh ten of them, and dry them 

 carefully in a water-bath to ascertain the amount of water which 

 they contain. Take two other lots of ten each, weigh them 

 carefully, plant them on moist blotting-paper or wet sponge, and 

 keep them in a warm place until the}' have sprouted. When 

 the beans have fairly started, suspend them over the surface of 

 water, with their roots in it, as directed in 669. From this time 

 on, keep one set of the seedlings in the light and the other set 

 in the dark, being careful in each case that the water is supplied 

 in sufficient quanthVy to make up for all loss by evaporation, and 

 that it is changed every third day. Let all the conditions under 



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which the two sets are cultivated be as nearly alike as possil Q 9 

 with the single exception that light is present in one case and 

 completely absent in the other. In a couple of weeks the two 

 sets of seedlings will have become large enough for further 

 study : the set grown in the light will be green and thrifty, the 

 others may be as large, but they will have a yellow, unhealthy 

 appearance. Remove the two sets from the water and carefully 

 dry them separately over the water-bath as directed in the case of 

 the seeds. When they do not further lose weight, weigh carefully. 

 Compare the weight of the dried seedlings with the weight of 

 the dried seeds. 



III. THE CHIEF CONDITIONS OF ASSIMILATION. 



In the examination of these, repeat with great care the expel 

 ments detailed on page 305. 



IV. THE DEPENDENCE OF GROWTH UPON HEAT. 



This may be shown in the following manner : Take a sheet Oi 

 tin or zinc about 6 to 8 inches in width and 24 inches in length. 

 Turn up its ends at right angles 6 inches. Turn them once 

 more at right angles, rather less than half an inch at the top 

 and two and a half inches at the bottom. This last turn will 

 hold a sheet of glass which will form the fourth side of a box, 

 narrower by two inches at the bottom than at the top ; that is, 

 the glass side will not be vertical, but inclined. Cut out a piece 

 of wire-gauze of the right size for the bottom, and either solder 

 or rivet it in place. Fill this box with well-moistened sawdust. 

 Plant a row of six or eight large Windsor beans in regular order 



