LENGTH OF THE YEAR. 27 



It appears then that the functions of plants 

 have by their nature a periodical character ; and 

 the length of the period thus belonging to vege- 

 tables is a result of their organization. Warmth 

 and light, soil and moisture, may in some degree 

 modify, and hasten or retard the stages of this 

 period ; but when the constraint is removed the 

 natural period is again resumed. Such stimu- 

 lants as we have mentioned are not the causes of 

 this periodicity. They do not produce the varied 

 functions of the plant, and could not occasion 

 their performance at regular intervals, except the 

 plant possessed a suitable construction. They 

 could not alter the length of the cycle of vegeta- 

 ble functions, except within certain very narrow 

 limits. The processes of the rising of the sap, of 

 the formation of proper juices, of the unfolding 

 of leaves, the opening of flowers, the fecundation 

 of the fruit, the ripening of the seed, its proper 

 deposition in order for the reproduction of a new 

 plant ; all these operations require a certain por- 

 tion of time, and could not be compressed into a 

 space less than a year, or at least could not be 

 abbreviated in any very great degree. And 

 on the other had, if the winter were greatly 

 longer than it now is, many seeds would not 

 germinate at the return of spring. Seeds which 

 have been kept too long require stimulants to 

 make them fertile. 



If therefore the duration of the seasons were 



