260 



FUNCTIONS OP FLOEAL ENVELOPES. 



opened on the 14th of March ; the discharge of pollen commenced on 

 the 16th, and continued till the 18th. The maximum temperature 

 occurred at a different hour on each day. 



14tli March. 

 15th „ 

 16th „ 



Maximum. 



3 P.M. 



4 „ 



5 „ 



Temperature 

 above the Air. 



4-6° Cent. 

 10-0° „ 

 10-2° „ 



17th March. 

 18th „ 

 19th „ 



Maximum, 

 5 P.M. 



11 A.M. 



10 „ 



Temperature 

 above the Air. 



11-0° 

 8-2° 

 2-5° 



Cent. 



Vrolik and De Vriese made a series of observations on the same 

 plant, and have given the results for every half-hour of the day. The 

 following are some of these results : — 



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 

 maximum occurred at 3 p.m., and on the following day at 1, but then 

 it was only 8'2° above that of the air. Decan4olle states that at Mont- 

 pellier, Arum italioum attained the maximum of temperature about 5 

 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 ladicans, from 0'9° to 3°. From all these experiments it 

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

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

 duction of heat, which increases during the performance of their 

 functions, attaining a daily maximum, and ultimately declining. 



While these changes are taking place the starch is converted into 

 dextrin, and ultimately into grape-sugar, which, being soluble, can be 

 immediately applied to the purposes of the plant. 



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

 existence. The process requires a considerable amount of nutrient 

 matter, and its occurrence is accompanied by a greater or less ex- 

 haustion of the assimilated products. 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, 

 time is allowed for accumulating sap, the stems, from being herbaceous, 

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

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



