THE STEM OF VASCULAR PLANTS. 177 



another, the stem remains as if its top were cut off, and 

 it produces several branches at the same point : if it pro- 

 duce two it is said to be Forked, or, when the phe- 

 nomenon is repeated several times, Dichotomous ; if 

 three be developed, the stem is Trifurcated, or Tri- 

 CHOTOMOUs, &c. Fig. 1, PI. 5, is taken from a trifur- 

 cation of a branch of the Chestnut, and may give an idea 

 of the phenomenon I have described. It may also be 

 very well observed in the Lilac. 



Art. IV. — Of the Increase of Exogenous Stems 

 IN Length and Diameter. 



I have already occasionally related, in speaking of the 

 Woody and Cortical Bodies, the principal facts relative to 

 the growth of stems ; it is necessary to repeat them a 

 a little more in detail, and to see in what point they 

 can be referred to any theory. 



Every stem, or branch, springs from a germ, at 

 first very small, which, in developing, only dilates ; so 

 that all the parts visible after its entire development, 

 appear to exist in miniature at the time when it was 

 first perceived. I do not discuss here either the origin 

 of the germs, or the general question of the formation 

 of beings ; I am only bound to express a fact, such as 

 observation gives it. 



The part which may be considered as the development 

 of a germ, elongates to a certain limit, determined by the 

 necessary time for the fibres to acquire the degree of 

 firmness peculiar to their nature : stems or branches 

 usually acquire this at the end of the first year of 

 their life. When marks are placed at equal distances 



VOL. I. N 



