CONDITIONS OF GAMETE FORMATION 375 



s 



regions. In consequence of this condition the flower may be 

 expected to show a relatively high rate of respiration. 



The accumulation of organic material and the relatively low 

 metabolic rate in the vegetative parts of the plant are probably 

 factors in making possible the high rate in the flower, which develops 

 at the expense of the nutritive substances in other parts. The 

 flower is a new individual or system of individuals, which arises 

 under conditions of low metabolic rate in other parts, and such 

 conditions favor the establishment in it of a high rate of metabolism 

 and growth. Evidently the flower is a more stable structure than 

 most of the vegetative parts of the plant and it undergoes rapid 

 progressive differentiation and aging. These characteristics are 

 also doubtless associated, on the one hand, with metabolic condition 

 of advanced age in other parts and, on the other, with its own high 

 metabolic rate. 



In most flowers the rate of respiration decreases from relatively 

 early stages onward, but in some cases it undergoes increase or 

 remains almost constant up to the time of opening. These differ- 

 ences are probably associated with differences in the size and 

 amount of growth of the ovary and its contents as compared with 

 other parts of the flower. It was suggested in the preceding chap- 

 ter (pp. 349-50) that the increase in rate of respiration in the pistil 

 during its development is connected with the increasing bulk of the 

 growing ovules and embryo sacs in proportion to the whole pistil. 

 Since it is impossible to measure the respiratory rate of single game- 

 tophytes (pollen grains or embryo sacs) or gametes during their 

 development, the available data on rate of respiration in the flower 

 and its parts are incomplete for present purposes. In the case of 

 the pistil particularly they represent measurements of rate in a 

 complex system in which different parts attain their maximum 

 activity at different times and differ in amount and rate of growth 

 in different cases. Nevertheless, so far as the data are applicable 

 they do not conflict with, but rather support, the view that the 

 flower is a product of relatively advanced physiological age in the 

 plant. 



In those cases where blooming is periodically repeated in the life 

 of the plant, as in perennials, it must be remembered that new 



