34 STUDIES IN PHYSIOLOGY. 



of good specimens of Drosera rotundifolia, the facts there re- 

 corded. Students are reminded that Mi\ Darwin's observations 

 were made with the simplest appliances, and with a degree of 

 care never excelled. 



For independent study abundant material may be found in the 

 common Sarracenias of the North and South, in regard to which 

 very much still remains to be learned. 



XXI. CROSS-FERTILIZATION. 



For this study, repeat the observations of Darwin as they 

 are given in his work on Cross and Self Fertilization ; or if that 

 is not at hand, as they are briefly stated in the abstract in the 

 present volume, pages 448-450. 



XXII. HYBRIDIZING. 



With the precautions given on page 456 the student should 

 be able to undertake experiments in hybridizing species of the 

 following common genera, all of which lend themselves readily 

 to this process : Nicotiana, Verbascum, Lilium, etc. Be care- 

 ful to exclude foreign pollen in all cases. 



XXIII. THE RIPENING OF FRUITS AND SEEDS. 



Good material for this stud} 7 is afforded by the following 

 plants : Solanum, Irnpatiens, Pyrus, Prunus, and Tecoma. 



XXIV. GERMINATION. 



Select sound seeds of some common plant, for instance beans 

 or Indian corn, and test with them the truth of the following- 

 statements : (1) Water is essential to germination. (2) Germi- 

 nation cannot begin without access of free ox}-gen. (3) Seeds 

 of the plants selected require the same temperature for the be- 

 ginning of germination. (4) When the process of germination 

 has once begun, light is necessary to any increase of the plant in 

 diy substance (compare experiment Series 1, No. II.). (5) Car- 

 bonic acid is constantly given off during germination. (6) In 

 some cases carbonic acid will continue to be evolved even when 

 no more oxygen is supplied (compare intramolecular respira- 

 tion). (7) The temperature of germinating seeds is higher than 

 that of the surrounding atmosphere (compare respiration). 



What is the optimum amount of water required for the speed}' 

 germination of the following seeds, - -Windsor beans, peas, 

 clover, squash, and sunflower? 



