18 VEGETABLE LIFE. 



it is only the union of heat, air, and water in due 

 proportions, tog-ether with the influence of light, 

 which can prompt vegetable life into perfect action. 

 The regermination of trees, and all the vernal 

 movements of plants, are usually and properly as- 

 cribed to the improved temperature of the season. 

 Yet we cannot suppose that higher temperature is 

 the sole cause ; for this reason many plants, instead 

 of being carried along by the increasing heat of the 

 summer, actually become torpid at the end of spring. 

 Such are almost all our bulbs and tubers cultivated in 

 the flower garden: and such are the first to com- 

 mence a new growth in autumn, and even put forth 

 their flowers in winter. As the precocious move- 

 ments exhibited by many bulbs, tubers, and some 

 of the amentaceous plants, cannot be attributed 

 to increased temperature, what reason can we assign 

 for this their seemingly premature evolution ? It may 

 be answered, that every plant is so constituted as 

 best suits the purposes of reproduction. Bulbous, 

 or other protuberances of the stem, are no other 

 than safeguards to the vitality of the plant during 

 the heat of summer ; for during that time it is dor- 

 mant, and continues so till the setting in of the 

 autumnal rains, when the temperature is every day 

 declining ; so that the decreasing heat, which arrests 

 the growth of almost all other plants, affects not 

 bulbs. This is owing, no doubt, to the constitutional 

 formation of the bulb, its seat of life is centrally 

 posited, and defended by a thick investment of 



