142 On Changes of Temperature in Plants. 



for by its greater abundance. The young branches, containino' 

 a much greater quantity of water, suffer more from cold. 



The results of experiments made upon a great number of 

 plants, with the view of discovering the quantity of water which 

 their leaves contain, are then detailed. Trees and shrubs have 

 much less water than herbaceous plants. If the former contain 

 from 54 to 65 parts in the hundred, the latter contain from 65^ 

 to 70, and even 88 parts. Succulent plants present from 90 to 

 95 per cent. The floral leaves generally contain more watery 

 parts than the stem leaves. The quantities of water contained 

 in the leaves of a great number of plants are presented in a table. 

 Another table shews a certain number of vegetables, on which 

 observations have been made for determining the velocity with 

 which their leaves emit their aqueous parts. The species which 

 present the most rapid evaporation, are those which require the 

 greatest quantity of water in vegetating. If the carices, the 

 gramineae, and the aquatic plants, evaporate in a short time, the 

 large quantity of water which they contain ; the succulent plants, 

 on the contrary, give it out but very slowly, for which reason 

 they vegetate easily in the warmest countries. The coniferae,^ 

 and shrubs with coriaceous leaves, resemble the succulent plants 

 in respect to the slowness of their evaporation. Very interest- 

 ing researches by the author have proved that the quantity of 

 water given out by evaporation in the gramineas, is, in a given 

 space, in some cases, two or three times more than that evaporated 

 by an equal surface of water. Sedtim album, on the contrary, 

 submitted to the same experiment, did not evaporate more than 

 half the quantity given off by water. 



In three tables, there are given inquiries respecting the thick- 

 ness of the concentric layers, in 24 species of trees of the forests 

 of EssUngen, where M. Neuffer examined them ; the weight of 

 newly cut wood, compared with that of wood carefully dried ; 

 and the specific weight of each kind of wood. The treatise con- 

 cludes with a table, indicating the degree of cold which a consi- 

 derable number of plants can support in our climates. Professor 

 Schubler has made most of these experiments, and has compared 

 them with those made in different botanic gardens. This trea- 

 tise has afforded us the greatest pleasure, and we think it de- 

 serving of the attention, not only of physiological botanists, but 

 also of agriculturists. 



