182 



manifest itself more or less slowly. They are given by the budding 

 of the Galantus nivalis^ of thei Crocus vernus, by the appearance of 

 the catkins of the Corylus avellana^ of the leaves of the Rihes grossu- 

 laria^ of the Samhucus nigra^ of the honeysuckle, and of some spireas. 



The falling of the leaves is also determined by the temperature, 

 and in our climate generally takes place after the first frosts. This 

 period and that previously mentioned come ordinarily at the two 

 limits of Avinter, and they separate to make place for the different 

 stages of vegetation in proportion as the cold of winter has a less 

 duration. The winter sleep lasts in our climate from three to four 

 months; in southern countries it is very much shorter. We can even 

 imagine a line on the surface of the globe where it ceases altogether 

 for the generality of plants." 



The great movement of vegetation commences in Belgium in the 

 middle of March and terminates at the end of April. I will call 

 this the period of leafing (feuillaison), because during this interval 

 the different plants are covered with their v^erdure and some of them 

 show their first flowers. 



The second period is that of flowering (floraison), which in our cli- 

 mate would include the months of May and June and the first half 

 of July. 



The third period would then come, Avhich is that of ripening 

 (fructification). 



These three great periods should undoubtedly be in their turn sub- 

 divided, but the present state of the observations does not allow 

 of such detail. It is understood, moreover, that the names T have 

 given to them only serve to designate the principal phases of vege- 

 tation which take place. Thus, in making the general table [omit- 

 ted— C. A.] I have classed the different plants according to the 

 following seasons : 



Awakening of the plants. — This period is determined by the plants 

 comprised in the [omitted] table. 



Leafing. — This period comprises the plants which, in Brussels, 

 put out their leaves from the 15th of March to the 30th of April, 

 and Avhich bud during the same two months. 



Flowering. — I have made use of the plants which have flowered or 

 brought forth their fridt from the 1st of May to the 15th of July. 



o As I have already observed elsewhere, the awakening is an epoch that is not 

 the same for all plants. I mean to speak here only of the epoch when the sap 

 begins to circulate in the majority of the plants which grow in our climate. 

 'All plants do not begin to vegetate at the same period," says M. Ch. Martins, 

 in the Botanical Expedition along the Northern Coasts of Norway. " Thus in 

 some the sap begins to mount when the thermometer is only a few degrees above 

 zero (centigrade) ; others need 10 or 12 degrees of heat, while those in warm 

 climates require a temperature of from 15° to 20° C. In a word, every plant has 

 its own thermometric scale, whose zero corresponds with the minimum tempera- 

 ture at which vegetation is possible for it. Consequently, when we wish to deter- 

 mine the sum total of the temperature that has determined the date of tlowering 

 (fleuraison) of each of these plants it is logical to only consider for eacli plant 

 the sum of the degrees of temperature above zero (centigrade), since these tem- 

 peratures are the only ones that have been efficient in inducing or sustaining 

 their growth." In tropical countries the great fluctuations in the vegetable king- 

 dom are not regulated by the same meteorological elements as are effective with 

 us; there the rainy season produces very nearly the same effects as the cold 

 season does in our climates. 



