78 TPIE MECHANICAL FUNCTIONS. 



The developement of each branch takes place in 

 the same manner, and by the same kind of process, 

 as that of the trunk. The buds from which they 

 originate, spring from the angle formed by the 

 stalk which supports a leaf, and which is termed 

 by botanists the axilla of that leaf. A law of sym- 

 metry is established by nature in the developement 

 of all the parts of plants. The leaves, in particular, 

 are frequently observed to arise in a circle, or sym- 

 metrically round the parent stem ; forming what is 

 termed a whorl, or, in botanical language, a verti- 

 cillated arrangement. In other cases they are found 

 to have their origins at equal intervals of a spiral 

 line, which may be conceived to be drawn along 

 the stem or branch from which they grow. When 

 these intervals correspond to the semi-circumfe- 

 rence of the stem, the leaves alternate with one 

 another on its opposite sides. 



The stems of most plants, even those which are 

 perfectly erect, exhibit a tendency to a spiral 

 growth. This is observable in the fibres of the 



tion of individual buds, each bud being a distinct individual plant, 

 and the vi'hole tree an aggregation of such individuals. 



These speculations have been carried to their extreme limit by 

 Schleiden, who regards every one of the cells, which compose the 

 vegetable tissue, as possessing an independent life; and the plant 

 itself as an aggregate of fully individualized independent beings, 

 namely, the cells themselves. See Taylor's Scientific Memoirs, II. 

 281. Mirbel adopts the same views; for he says, speaking of the 

 vegetable cells, " II ne parait pas que jamais il s'etablisse entre elles 

 une veritable liaison organique. Ce sont autant d' individus vivants, 

 jouissant chacun de la propriete de croitre, de se multiplier, de se 

 modifier dans de certaines limites, travaillant en commun a I'edifica- 

 tion de la plante, dont ils deviennent eux-memes les materiaux 

 constituants. La plante est done un etre collectif." Ann. Se. Nat. 

 serie 2. Bot. xi. 325. 



