CHAPTER XIII 



PHYSIOLOGICAL PROCESSES DURING FLOWERING 

 AND RIPENING OF FRUITS AND SEEDS 



99. Physiological Processes during Blooming. Respiration of 

 Flowers. Nyctinastic and Seismonastic Movements.— It is 

 known from studies of plant morphology that flowers represent 

 modified shoots adapted to the functions of reproduction. The 

 external parts of the flower, chiefly the calyx and in a lesser 

 'degree the corolla, representing leaves that are very httle modi- 

 fied, participate in photosynthesis in their early stages of devel- 

 opment owing to the presence of green plastids. From the 

 time of the opening of the flower, this function becomes sub- 

 ordinate, and respiration becomes intensive. Flowers that are 

 opening have been used like germinating seeds for demonstrating 

 the respiration of plants. In massive flowers such as those 

 of the aroids or of the gigantic water hly Victoria regia, a con- 

 siderable increase in temperature takes place because of rapid 

 oxidation. Such intensive respiration is accompanied by a 

 considerable consumption of organic substances. Many authors 

 who have studied the accumulation of dry substance of plants 

 during their vegetative period have noted a marked decrease in 

 the total weight of the plants during blooming, which may be 

 due to cessation of vegetative growth at this time, to decreased 

 photosynthesis, or to both. In perennial grasses and in woody 

 plants, blooming usually occurs in the spring and is accompanied 

 by utilization of the reserves stored during the previous summer. 

 Annual plants also show a considerable depletion of food reserves 

 of the stems and leaves at the time of blooming. This depletion 

 usually reaches its maximum at the time of ripening of the fruit 

 and seeds. Hence, in utilizing natural and cultivated meadows 

 for hay, the grass must be cut at a time not later than the begin- 

 ning of blooming of the grass varieties that predominate in 

 the meadows; otherwise there will be considerable losses in the 

 total amount of nutritive substances. 



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