232 FUNCTIONS OF FLORAL ENVELOPES. 



same plant, and have given the results for every half hour. The fol- 

 lowing are some of these results: 



2-30 26-5 15-6 i 



The greatest amount of heat observed was at 2-30 P.M., when it was 

 10 '9 above the temperature of the air. On the previous day the maxi- 

 mum occurred at 3 P.M., and on the following day at 1, but then it 

 was only 8 '2 above that of the air. Decandolle states that at Mont- 

 pelier, Arum italicum attained the maximum of temperature about f> 

 P.M. Saussure observed similar phenomena, but to a less extent, in 

 the Gourd, where the temperature varied from 1'8 to 3 '6; also in 

 Bignonia radicans, from 0*9 to 3. From all these experiments, it 

 would appear that in the Araceas and some other plants, especially at 

 the period when the essential organs reach maturity, there is a produc- 

 tion of heat, which increases during the performance of their functions, 

 attaining a daily maximum, and ultimately declining. 



477. While these changes are taking place, the starch is converted 

 into dextrine, and ultimately into grape-sugar, which, being soluble, 

 can be immediately applied to the purposes of the plant. The honey- 

 like matter thus formed is stored up frequently at the base of the 

 petals, in little pits or nectaries, as in Fritillary, Asarum, &c. It is 

 considered by Vaucher and others as performing an important office in 

 fertilization, covering the stigma, and aiding in the dispersion and rup- 

 ture of the pollen-grains. Bees and other insects, in collecting the 

 saccharine matter, also scatter the pollen. 



478. Flowering takes place usually at a definite period of the plant's 

 existence. It requires a considerable amount of nutrient matter, and 

 its occurrence is accompanied with a greater or less exhaustion of the 

 assimilated products. Hence, a certain degree of accumulation of sap 

 seems necessary in order that flowering may proceed. Annual plants 

 are so exhausted after flowering as to die; but, by retarding the epoch 

 for two or more years, as by nipping off the flower-buds, tune is 

 allowed for accumulating sap; the stems, from being herbaceous, be- 

 come shrubby, and sometimes, as in the Tree-Mignonette, they may be 

 made to live and flower for several years. Perennial plants, by the 

 retardation of flowering, are enabled to accumulate a greater amount 

 of nutritive matter, and thus to withstand the exhaustion. Many cul- 

 tivated plants, which lay up a large store of nutriment in the form of 



