THE VEGETABLE CELL. 145 



upward and grow in tlio vertical direction in the manner of the trunk, of 

 whicli large specimens of Finus Cmiihra in particular exliibit tlie mobt 

 beautifiil and striking examples. 



To Butrochet belongs tlie merit of having called attention to tlie dif- 

 ference between tlie organization of the stem and the root, which must 

 incontestibly be taken into consideration before all else, in discussing the 

 movements now referred to, and gives hope that their further investiga- 

 tion will solve much that is still doubtful in respect to the movementb of 

 plants. Dutrochet {^^ Memoires^' ii. 1) endeavoured to trace the curva- 

 ture of the stem upward and that of the root downward from the endos- 

 mose exercised in the parenchymatous cells of these organs. He found 

 that a plate cut longitudinally, in the direction of a radius, from an her- 

 baceous stem, curved in water so as to render the epidermis concave ; 

 while a plate cut out of a young root exhibited the opposite curvature. 

 The cause of these different curvatures he found, in the decx-easing size of 

 the pith-cells from within outwards in the stem (these alone coming into 

 consideration on account of the preponderating size of the pith and the 

 proportionately small thickness of the bark), and in the decreasinfi^ size 

 lol witW Lwax-ds of the cortical oaUs o'f the root, these alone Seing 

 of importance in regard to the root where the rind is so much more deve- 

 loped. This tendency to curve exists, although in less degree, when the 

 different parts are not placed in water, in consequence of the cells being 

 full of sap, as in the natural condition of plants. The different sides of 

 the root and stem possess the tendency to this cmwature in an equal 

 degree so long as these organs are in a perpendicular position, and thus 

 the force of one side is kept in equilibrium by that of the opposite side. 

 But when a stem or root is placed in an inclined position, according to 

 Dutrochet's view, the effect of gravity causing a flow of the concentrated 

 sap toward the lower side of the organ, limits the endosmose exercised 

 hj the cells of this side^, while the cells of the upper side which come in 

 contact with a less concentrated sap are unrestrained in their endosmose, 

 and in their expansion consequent therexipon. Thus the tendency to 

 curvature arising from the endosmose in these acquires the preponderance, 

 and causes an upward curvature of the stem and a downward of the root. 

 iNotwitbstanding that many errors occur in the statements of Dutrochet's 

 treatise, and that the manifold modifications which present themselves in 

 the directions of stems and shoots in different plants, a few only of wMch 

 have been indicated above, cannot as yet be explained from their struc- 

 ture, yet this author has the credit of having demonstrated the element- 

 ary truths : 1, That the curvature of the root and the stem is independ- 

 ent of their growth ; 2, That the moving organ must be looked for in 

 the soft parenchymatous cells ; and 3, That the curvature effected hj the 

 cells is not produced by a contraction of that side which becomes con- 

 cave, thus drawing over the other part of the organ, but, on the contrary, 

 the curvature arises from a swelling of that side of the organ which be- 

 comes convex. 



Both stem and root are only capable of retaining the perpen- 

 dicular direction which they assume through the influence of 

 gravity, when they are wholly removed from light, or light is 

 freely admitted to all sides of tliem ; when the light shines only 



h 



