SECT. I. EXCITABILITY, 44 Q 



SUBSECTION II. 



Action of Heat. Heat as well as light acts also 

 as a powerful stimulus to the exertion of the vital 

 principle. This has been already shown in treating 

 of the process of germination, in which it was found 

 that seeds will not germinate at a very low tem- 

 perature, even though placed in a proper soil, so that 

 such as sow themselves do not generally come up 

 till the spring when the temperature has been raised 

 to some considerable height by the rays of the re- 

 turning sun. But the same thing is observable As influ- 

 with regard to the developement and maturation of protrusion 



the leaves, flower, and fruit ; for although all plants 

 produce their leaves, flower, and fruit, annually, yet and frulU 

 they do not all produce them at the same period 

 or season. This forms the foundation of what Lin- 

 naeus has called the Calendarium Flora, including 

 a view of the several periods of the Frondescence 

 and Efflorescence of Plants, together with that of the 

 Maturation of the Fruit. 



ART. 1. Frondescence. It must be plain to every Seasons 

 observer that all plants do not protrude their leaves different 

 at the same season, and that even of such as doP lants 

 protrude them in the same season, some are earlier 

 and some later. The Honeysuckle protrudes them 

 in the month of January ; the Gooseberry, Currant, 

 and Elder, in the end of February or beginning of 

 March ; the Willow, Elm, and Lime-tree, in April; 



VOL. II. 2 G 



