712 ORDERS OF ANGIOSPERMS. 



The thistle family (Compositae) includes the thistle (Carduus), 

 asters (Aster), goldenrods (Solidago), sunflowers (Helianthus) , 

 eupatoriums or joepye- weeds, thorough worts (Eupatorium), 

 cone-flowers or black-eyed Susans (Rudbeckia), tickseed (Core- 

 opsis), bur-marigold or beggar-ticks or devil's-bootjack (Bidens), 

 chrysanthemums, etc. 



Absorption by aquatic plants through roots (see paragraph 952). 

 Aquatic plants which are rooted to the soil in a number of cases have been 

 found to have root hairs. Experiment has demonstrated in these cases 

 that mineral foods are largely taken from the soil and not from the sur- 

 rounding water. Examples of such plants are Vallisneria spiralis, Ranun- 

 culus aquatilis, Elodea canadensis, Potamogeton perfoliatus. The latter 

 made 480 per cent better growth when rooted in soil than when rooted in 

 sand. Such plants, therefore, taking their mineral food from the soil, 

 when they decay increase the amount of food for the plankton or floating 

 plants, or those merely anchored but without well-developed roots or root 

 hairs. See Pond, Raymond H., Biological relation of aquatic plants to 

 the substratum, U. S. Fish Commission Report for 1903, pp. 483-526, 

 1905. Also, How rooting aquatic plants influence the nutrition of the 

 food fishes of our Great Lakes, Pop. Sci. Month., pp. 251, 254, 5 figures 

 in text, March 1906. 

 To prepare Fehling's solution. Make up two stock solutions as follows: 



( Copper sulphate 34. 639 grams. 



( Distilled water 500 cc. 



C Sodium hydroxide (caustic soda sticks) 50 grams. 



B < Rochelle salts 1 73 grams. 



( Distilled water 500 cc. 



When ready to use, prepare Fehling's solution by mixing equal volumes 

 of A and B. If the Fehling's solution is old, or has sediment, bring it to 

 boil for a minute or two and filter. 



Another formula for the stock solutions is as follows: 



( Copper sulphate 9 grams. 



( Distilled water 250 cc. 



Potassium hydroxide (caustic potash sticks) 30 grams. 



Distilled water 250 cc. 



Rochelle salts 43 grams. 



Distilled water 250 cc. 



When ready to use, make Fehling's solution by taking equal volumes 

 of each i, 2 and 3, and to the mixture add an equal volume of dis- 

 tilled water. If old or there is a precipitate, boil and filter. 



