478 X. GENEEAL REMARKS. 



equal by the simple process of taking in oi* striking out a 

 few more of the thermometrical degrees. For most spe- 

 cies it will be found too uncertain — that is, too optional — 

 at what precise degree of the thermometer the plant com- 

 mences, continues, or ceases to develope. Roots, leaves, 

 flowers, fruits, all require different degi-ees of temperature 

 for their development, and applied unequally at different 

 stages of their growth. 



It is difficult to suggest any practicable mode of ob- 

 serving and recording instrumental indications of tem- 

 perature, which would be adapted to the varying require- 

 ments of plants, regarded in this manner. In the same 

 country, at the very same time, various species may be in 

 all the different stages of growth, from germination to 

 maturation, from absolute torpidity to vigorous develop- 

 ment. While the snowdrop is flowering in our gardens, 

 the buds of the oak are dormant. And while the oak- 

 flower is slowly developing into the perfect acorn, the 

 snowdrop becomes torpid ; resuming its growth about the 

 date when the acorn falls ; and doing so earlier if the 

 ground becomes damp, later if it continues dry, almost 

 irrespective of temperature at a season when uniformity 

 prevails. The colchicum and the daffodil are at rest for 

 a very short period of the summer's warmth and dryness. 

 During nearly the same period the leaves of the white 

 hellebore are still growing ; its flower-buds appearing 

 later in the autumn, and expanding into blossom in the 

 midst of winter ; whence its familiar name of the ' Christ- 

 mas Rose.' And among the species which follow a more 

 usual course of development, by commencing to grow in 

 spring and ceasing in autumn, the dates of commence- 

 ment and cessation, and consequently also the degrees of 

 useful temperature, can scarcely be specified. 



