Imperial Institute of Frnnce. 383 



lowest verticille, from which a leaf and a bough frequently 

 fall off, there will be two angles only, and the vestige of a 

 third equally abortive. This law is constant, even in the 

 herbaceous plants. 



M.de Bt-auvois has begun similar observations on the plant s 

 with opposite leaves, those alternating, distic, repeated spiral, 

 and composed of four, five, and a greater number of boughs 

 and leaves. He thinks it probable that there are the same 

 relations between the form of the medullary canal and the 

 disposition of the branches, the boughs, and the leaves. 

 For example, the opposite leaves stem to necessitate a 

 round medullary canal, and which becomes oval, having the 

 extremities more and more acute the nearer it approaches 

 the point of insertion of the boughs and leaves. 



When the leaves are alternate, the circle is less perfect, 

 the extremities are thinned off equally, but alternately, and 

 each on the side on which the bough ought to appear. 



When the leaves are spiral, the number of the angles of 

 the medullary canal is equal to that of the leaves of which 

 the spirals are composed. It is thus that the medullary 

 canal of the linden tree has only four angles ; that of the 

 oak, the chcsnut tree, the pear, and alniost all fruit-trees, 

 &c. has five angles more or less regular, because the spirals 

 are multiplied, and succeed constantly by fives. 



Grew and Bonnet seem to have been the first to make 

 these observations. The former had observed very singular 

 forms in the medullary canal, particularly in that ot the 

 pivoting roots of pot-herbs; but he has not seized the re- 

 lations of these forms with the dispositions of the boughs 

 and the leaves. The latter directed his attention to distin- 

 guish the vegetables with opposite leaves verticillated, al- 

 ternated, spiral, but has not. made a comparison of these 

 dispositions with the form of the medullary canal. 



M. de Mirbel has continued his researches in the stroc- 

 ture of the organs of fructification in vegetables, in which 

 he has been most zealously seconded by M. Schubert, who 

 was sent to France by the Government of Warsaw to ac- 

 quire the science of botany preparatory to his publicly 

 leaching it in Poland. 



These two botanists have examined all the genera of the 

 family of the prickly trees, or the couiferae; trees of the 

 first importance, on account of the singularity of their or- 

 ganization, the magnitude of the species, and the utility of 

 their products. Every person can distinguish at the first 

 glance the cedar, the pine, the yew, the juniper, &c.j but 

 althotigh botanists have studied with particular attention 



the 



