182 
manifest itself more or less slowly. They are given by the budding 
of the Galantus nivalis, of the Crocus vernus, by the appearance of 
the catkins of the Cor ylus avellana, of the leaves of the Ribes ¢ GV Ossu- 
lavia, of the Sambucus 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 winter, 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 1s 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 verdure 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, which 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 1s understood, moreover, that the names I have 
given to them only serve to designate the principal phases of vege- 
tation which take place. Thus, in making the general table fomit- 
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. 
Leajfing—This period comprises the plants which, in Brussels, 
put out their leaves from the 15th of March to the 30th of April, 
and which bud during the same two months. 
Flowering.—I have made use of the plants which have flowered or 
brought forth their fruit from the Ist of May to the 15th of July. 
a 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. Ina word, every plant has 
its own thermometri¢ scale, whose zero corresponds with the minimum tempera- 
ture at which vegetation is possible for it. Consequently, when we wish to deter- 
inine the sum total of the temperature that has determined the date of flowering 
(fieuraison) of each of these plants it is logical to only consider for each 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- 
com 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. 
