00 STRUCTUrvK AND PIIYSTOl.OGY OF SEED PLANTS 



and describe the main differences in color, height, and thickness 

 of hypocotyl, and in the development of the cotyledons of those 

 grown in darkness and in the light. 



What is the conclusion in regard to power to make chlorophyll ? 



Leave both lots in sunlight for a day and test some cotyle- 

 dons of each set for starch. Leave both sets in sunlight for 

 several days more and note any changes in the appearance of 

 those which were started in darkness. Test the latter again for 

 starch. Conclusions ? 



Reference. Pfeft'er-Ewart, 31, II. 



EXPERIMENT XXXVI 



Do leaves give off water ? If so, from which surface is it given off 

 more abundantly? * * Fasten two small watch glasses, one on each 

 side of a leaf of a plant growing vigorously in a pot or out of doors. 



Fig. 4. Watch glasses fastened on a leaf of Chinese primrose 



Hydrangea,^ primrose, or cineraria ^ are good plants for the pur- 

 pose, although many others will answer. The watch glasses may 

 be held in place by a spring clip, as shown in Fig. 4. Seal the 

 margin of each glass all the way around by means of vaseline or 

 barely melted grafting wax. Leave the plant for half an hour or 

 more in a sunny place, and then look for drops of water inside 

 1 H. Hortensia. 2 Senecio cruentus. 



