PHOTOSYNTHESIS 



95 



52, dispute Sachs' interpretation of the increased weight in this experiment, 

 holding it is due to a more free admission of carbon dioxide through more 

 widely open stomata. 



Viewing the foregoing studies rather broadly, it may seem 

 to the student that while the formation of starch has been shown 

 to be accompanied by an increase in weight in the leaves, this 

 increase may simply represent material drawn from the stem, 

 and not new material added to the plant. If practicable it 

 wijl be of interest to test this possibility, which may be done by 

 including entire plants in the experiment, instead of leaves only, 

 though it may also be accomplished by the use of leaves severed 

 from the plant. 



Sxjggested Experiments. To obtain comparative weights of organic 

 substance in different entire plants, it is obviously necessary to eliminate 

 the soil, which can be done by growing the plants through water-culture 

 methods, which are described by Detmer, i, and others, and later in this 

 book (under Synthesis of Proteids). For the present purpose, however, it 

 may very readily and satisfactorily be accomplished as follows. Take three 

 sets, each of 100 seeds, of Japanese Buckwheat, Radish, or Oats, and weigh 

 each set to a milligram, preferably, though not necessarily, making the three 

 sets equal in weight. Keep one set in reserve, and spread each of the others, 

 after suitable soaking, in a five-inch flower-pot saucer thoroughly cleaned by 

 boiling. Set these saucers in crystallizing dishes of such a size that the sau- 

 cers rest on their projecting rims (Fig. 21). Keep the dishes supplied with 

 tap water, which will supply itself in 

 correct quantity, and filtered, to the 

 plants. Or a hydrostatic arrangement 

 may be used for the watering. Expose 

 the two sets of seeds to similar and good 

 growth conditions, preferably under simi- 

 lar bell jars, except that one set is 



screened from light. Keep them under FlG - 2I -~ Arrangement for spe- 

 constant care until those in the dark CIAL M0DE 0F water-culture, 

 have reached their limit of growth, which IN section; Xk- 

 will require three to five weeks according Seeds rest on * flower-pot saucer kept 

 to season. Remove the plants, with all wet by water in a cl T staIIiz tag dish. 

 seed-coats, etc., from the saucers, to which they will not adhere, place them 

 in suitable glass dishes, and dry them in the oven, together with the third set 

 of seeds, until they cease to lose weight. Then weigh them all carefully, 

 using the weight of the seeds to detenr ine the percentage of water originally 

 present in the seeds of the other sets, and determine the exact increase 

 or decrease of dry weight. Two apparent errors in the result, a loss from 



jVjT5T?.,.re 4£ 



