2084 Journal of Applied Microscopy 



graph to show how the lack of flatness of the field limits the area in which it is 

 possible to get a sharp focus. 



In using our method of focussing it is a great aid to determine the limits 

 within which a sharp focus can be expected, for it is easy to strain the eye to see 

 details beyond these limits ; the negative in this case giving disappointing results. 



We have not found it necessary to use color screens or the ray filter, as most 

 of our work is done with preparations stained in iron hematoxylin. If prepara- 

 tions with this stain are very much decolored, a short after stain of dilute Bis- 

 marck brown will give enough yellow tone to the preparation to afifect the sensitive 

 photographic plate and to insure a brilliant negative, although the color should 

 be so delicate as to be scarcely perceptible to the eye through the microscope. 

 Woods Hole, Mass. KATHARINE FoOT AND E. C. StR01!ELI,. 



METHODS IN PLANT PHYSIOLOGY. 



VI. 



VIII. CARBON ASSIMILATION. 



1. The Effect of Light upon Food Formation. Select three sets of five kernels 

 of corn (Zca Mais) so that each set has exactly the same weight. One set of 

 kernels is to be crushed in a mortar, and dried in an oven at U>ii°C. until they 

 cease to lose weight upon further heating; the flnal dry weight is recorded for 

 future comparisons. The other two sets are planted in separate crocks of damp 

 sawdust, and when the plumules have obtained a length of '1 cm. to ."> cm. the 

 seedlings are to be removed, carefully washed in distilled water, and placed in a 

 water culture containing a full nutrient solution as described on p. '1M\A of this 

 journal. The two jars are to stand side by side in the plant house, one in bright 

 light, the other deprived of all light. 



At the end of three or four weeks each group of seedlings is to be removed 

 separately, no part being lost, washed carefully in distilled water, all adhering 

 particles being removed, and the seedlings cut into small fragments with the 

 scissors. Place the fragments of each group in a small beaker, and determine 

 their dry weight as the weight of the kernels was previously determined. 

 Compare the weight of the plants with that of the ungerminated grains. If the 

 experiment has been successfully conducted there will be a decided gain in the 

 case of the illuminated plants, while the unilluniined plants will show only a small 

 gain, or possibly a loss. The difference in the two will serve to indicate the 

 amount of food formed by photosynthesis. 



2. Effect of Light on Starch Formation. Cover some leaves of the Nasturtium 

 {Tropcclum majus), or other suitable plant, with tin foil, allowing the covering to 

 remain for two days ; or a plant may be placed in the dark for two days. 

 Leaves that have been illuminated, and others that have been in darkness, are 

 removed from the plant in the afternoon, are killed by immersion in boiling 

 water, and placed in boiling 80 per cent, alcohol until the chlorophyll has been 

 extracted. The leaves are then to be placed on a white plate and covered with 



